Diagnosis Of Ductal Carcinoma In Situ Research Articles

Mammography of suspicious calcifications among ductal carcinoma in situ and benign breast disease.

Most ductal carcinoma in situ (DCIS) lesions manifest early as calcifications, which could be benign or malignant. The classified group of suspicious calcifications among DCIS and benign breast disease is clinically important to early evaluate patient risk factors and plan treatment options. To compare imaging features of suspicious calcifications between DCIS and benign breast disease. A retrospective study of 101 suspicious calcifications was performed at Thammasat University Hospital from June 2011 to October 2020. The calcifications were surgically excised by mammography-guided wire localisation. The mammographic features of the suspicious calcifications were reviewed according to the fifth edition of the American College of Radiology Breast Imaging-Reporting and Data System lexicon. For comparing between two groups, the student t-test, Fisher's exact test and Mann-Whitney U test were used for statistical analyses. The logistic regression analysis was calculated for DCIS prediction. The pathologic results of all 101 suspicious calcifications were DCIS (30 cases) and benign breast disease (71 cases). Linear morphology and segmental distribution correlated significantly with DCIS (p = 0.003 and p = 0.024, respectively). After multivariable analysis, fine linear calcification still significantly elevated the risk of DCIS (odd ratios, 51.72 [95% confidence interval: 2.61, 1022.89], p-value of 0.01), however, the odds of predicting DCIS was not statistically significant different among any distribution. Ductal carcinoma in situ calcification has contrasting morphology and distribution features compared to benign breast disease. The calcification descriptor is considered an important implement for early diagnosis and distinguishes DCIS from other benign breast conditions. Calcification descriptor is considered an important implement for early diagnosis and distinguishment of DCIS from other benign breast conditions.

Abstract PO2-11-02: Incidence, treatment patterns and outcomes of breast cancer during the first year of the COVID pandemic: A population-based study

Abstract Background: The COVID pandemic created significant challenges in breast cancer (BC) care which were most pronounced during 2020 when screening and treatment access were reduced. The aims of this study were to evaluate and compare the incidence of BC, treatment patterns, and outcomes during the year 2020 versus the immediate pre-pandemic (2018 and 2019) period. Methods: Using data from the Surveillance, Epidemiology, and End Results (SEER) program, we calculated age-adjusted incidence rates of ductal carcinoma in situ (DCIS) and invasive BC during 2018, 2019 and 2020, with a 95% confidence interval (CI) for each. In the invasive BC cohort, we compared chemotherapy and radiation utilization by year. To account for potential misclassification of cause of death (COD) during the pandemic, we evaluated outcomes by overall survival (OS) in the invasive cohort, defined as time from BC diagnosis until death from any cause. To assess the impact of COVID, OS was truncated at 12 months from diagnosis for each year and we compared OS at 12 months for patients (pts) diagnosed with invasive BC in 2020 versus 2018 and 2019. OS was compared in a multivariable Cox model with diagnosis year 2020 as the reference. The Cox model was adjusted for age at diagnosis, race and ethnicity, sex, tumor grade, histology, stage, tumor subtype, surgery, radiation, chemotherapy, marital status, median household income, and rurality. Results: There were 37,834 DCIS diagnoses, and 199,594 invasive BC diagnoses between 2018-2020, with the distribution by year shown in the table. In 2020, the age-adjusted incidence of female DCIS decreased to 31.0 cases per 100,000, and the age-adjusted incidence of female invasive BC decreased to 166.6 cases per 100,000. As shown in the table, the incidence of male BC did not change. Among females, the relative reductions in incidence from 2019 to 2020 were: 15% for DCIS, 12% for stage I, 6% for stage II, 3% for stage III, and 2% for stage IV. Comparing 2020 to 2018-2019, we observed small absolute decreases in the proportions of pts who had surgery (2%) or radiation therapy (2.8%), and a small absolute increase in chemotherapy (1.4%) (p< 0.001 for each). These treatment changes were present across each individual stage. The table shows the 12-month OS rates for each year of diagnosis. COVID was the COD for 77 pts in 2020, 43 pts in 2019 and 0 pts in 2018. In the Cox model, there were no significant differences in the risk of death between pts diagnosed 2018 and 2020 (adjusted Hazard Ratio: 0.95; 95% CI, 0.90 – 1.01; p=0.13) or between pts diagnosed 2019 and 2020 (adjusted Hazard Ratio: 0.95; 95% CI, 0.89 – 1.01; p=0.08). Conclusions: During the first year of the pandemic, the incidence of BC decreased significantly, largely driven by a decrease in DCIS and early-stage diagnoses. Of interest, there was no stage shift observed with respect to the incidence of stage III or de novo stage IV disease, and no change in male BC incidence. We hypothesize that the observed trends are due to a reduction in screening, but this needs further study. It will be critical to evaluate future trends in cancer incidence beyond 2020, as it is possible that the reduction in early-stage diagnoses represent missed diagnoses that will be identified at a later stage in subsequent years. Finally, while there was no difference in 12-month OS by year of diagnosis, the true impact of the COVID pandemic on BC-specific outcomes will require further follow-up. Citation Format: Jose Leone, Julieta Leone, Michael Hassett, Rachel Freedman, Jorge Avila, Carlos Vallejo, Nabihah Tayob, Sara Tolaney, Nancy Lin. Incidence, treatment patterns and outcomes of breast cancer during the first year of the COVID pandemic: A population-based study [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO2-11-02.

Abstract PO4-26-02: Evaluation of Tumor Infiltrating Lymphocytes as a predictive biomarker of recurrence in patients with Ductal Carcinoma In Situ of the breast

Abstract Introduction: Ductal carcinoma in situ (DCIS) represents around 20% of early breast cancer diagnoses globally. Some studies evaluated risk factors associated with DCIS recurrence. Among these, age, surgical margins, comedonecrosis (CN), high nuclear grade, negative hormone receptors and HER2 expression stand out. Recent approaches have been evaluating the role of the immune microenvironment and its association with recurrence and progression of DCIS. Objective: To evaluate the association between Tumor Infiltrating Lymphocytes (TILs) in DCIS samples and disease recurrence. To characterize the immunological microenvironment of DCIS, analyzing the presence of TILs, “touching TILs” and desmoplastic reaction and their association with recurrence. Epidemiological, clinical, histological and immunohistochemical (IHC) characteristics were also evaluated. Methods: This is a retrospective cohort study with patients diagnosed with DCIS and treated at Sao Paulo State Cancer Institute and Hospital das Clinicas of University of Sao Paulo. We included women over 18 years old with a diagnosis of DCIS who underwent treatment from Jan/2007 to Dec/2020. Male patients, patients with a diagnosis of invasive or microinvasive disease in the anatomopathological examination of the surgical specimen or patients with history of any neoplasm were excluded. The main outcome was survival analysis according to the quantification of TILs, adjusted for potential confounders. For that, we collected data on age, presence of palpable mass, imaging findings, histological and IHC characteristics, such as expression of estrogen receptor (ER), progesterone receptor (PR) and hyperexpression of HER2, type of surgical approach, type of radiation therapy, use of endocrine therapy, length of follow-up, recurrence, and its type. Two pathologists evaluated TILS in the sample with the highest tumor representation and numerically quantified it as percentage. They also evaluated the presence of “touching tils” (lymphocytes in contact with the basement membrane) and desmoplastic reaction in the tumor stroma. Kaplan-Meier curves, log-rank tests and Cox regression models were used to evaluate survival. Chi-square tests were used to evaluate the association between categorical variables. Results: 283 patients met the eligibility criteria. Mean age of patients was 55 years. 15% had a palpable nodule at physical examination. Clustered amorphous microcalcifications were the most prevalent mammographic presentation, found in 41% of the patients. The most frequent histological and IHC features were cribriform presentation (73%) and ER positivity (86%), respectively. Desmoplastic reaction was absent in 10.5%, discreet in 51.9%, moderate in 24% and intense in 13.6% of the patients. Breast conserving surgery was performed in 189 patients, and 100 of them received adjuvant radiation therapy. Mean follow-up was 77.2 months, with a recurrence rate of 9.2%. We observed that tumors with focal necrosis (HR 6.4 [1.39-34.71] p 0.018) or CN (HR 4.53 [1.34 – 15.28] p 0.015) had higher risks of recurrence. Patients with a percentage value of TILs greater than or equal to 17% also had a higher risks of recurrence (HR 2.97 (1.17-7.51) p 0.02). These patients were mostly under 65 years of age (OR 0.45 [0.21 - 0.97] p 0.049). In a multivariate model, CN and TILs>17% remained significantly associated with recurrence (p=0.034 and p=0.035 respectively). There was a trend for invasive recurrence in 76.9% of the patients that relapsed when TILS were greater than or equal to 17% (p 0.062). “Touching TILs” were present in 12.9% of the patients but were not associated with recurrence (p=0.575). Conclusion: In our cohort, high value of TILs (>= 17%) and presence of CN were independently associated with DCIS recurrence. Our findings suggest that TILS are a prognostic immunological biomarker in DCIS and warrant further investigation in prospective trials to determine the most adequate cut-point. Citation Format: Camila Pasetto, Fernando Aguiar, Marcella Peixoto, Maira Doria, Bruna Mota, Jonathan Maesaka, Jose Roberto Filassi, Edmund Baracat, Rodrigo Gonçalves. Evaluation of Tumor Infiltrating Lymphocytes as a predictive biomarker of recurrence in patients with Ductal Carcinoma In Situ of the breast [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO4-26-02.

Abstract PO5-03-02: Ductal carcinoma in situ: An excess regard of the axilla?

Abstract Abstract: Ductal Carcinoma in Situ (DCIS) is a malignant proliferation of the epithelial inside the breast duct, which does not invade the myoepithelial layer and, therefore, does not have the capacity to generate metastases. [1]. However, an upstaging after surgery is possible, since there may be a concomitant invasive lesion that was not diagnosed in the pathological examination from biopsy, being discovered only after the surgical procedure [1]. In the pre-screening mammography era, DCIS was diagnosed. more commonly in symptomatic women presenting with a palpable nodule, papillary flow, or through an incidental finding on a breast biopsy [2], accounting for 1-2% of cancer cases. [3]. After the advent of mammographic screening, the incidence has considerably increased among asymptomatic women with mammographic changes such as calcifications. [4]. Nowadays the diagnosis of DCIS corresponds to 20-25% of biopsies secondary to screening mammographic changes. [1]. As we do know that the chance of axillary metastasis is potentially null, old series where axillary dissection (AD) was performed ipsilareral to the index tumor, axillary involvement was observed in less than 1% of cases [9]. Objectives: Our objective in this study was to describe in a single breast cancer reference center the surgical treatment of patients diagnosed with DCIS (mastectomy or breast conservative surgery – BCS). Methods: A retrospective analysis was made using the Pérola Byington Hospital’s database, from January 2011 to December 2019. During this period, 11,373 cases of breast cancer were treated int the institution and 812 (7.4%) were DCIS. Data was available and we could analyze 494 patients who underwent vacuum-guided biopsy guided by mammography or ultrasound and were diagnosed with DCIS and underwent surgical treatment at the Hospital. We grouped the patients into 3 age groups: under 40, 40-49, and 50 and over. In all groups, we had patients who underwent SNB using the patent blue technique or AD and were evaluated using the H&E method. It is not part of the Institutional protocol to perform IHC in axillary lymph nodes. We had also evaluated the type of surgery (BCS or mastectomy) in each age group. Results: DCIS was diagnosed through mammographic alterations in 62% of all cases and nuclear grade 2 was the most common, with 47%, followed by grade 3 and 1, 46% and 4%, respectively. In 2% of cases the data was missing. Comedoconecrosis was present in 78% of our specimens. BCS was the most frequently surgery performed (73% of cases), with the axillary approach being performed in 35% of these patients (32% for SNB and 3% for AD). While 27% of patients underwent radical surgery and in this group 92% were submitted to axillary approach (70% SNB and 22% AD). In the group of patients younger than 40 years, 74% of patients (17 out of 23 in total) underwent an axillary approach regardless of the type of surgery. When evaluating the predetermined age groups, we saw that most of our patients were 50 years or more (69%), followed by patients between 40-49 years (26%) and 5% in patients under 40 years. In 3% of cases (16 in 494) we reclassified the lesion as invasive carcinoma. None of them had a lymph node involved by malignant cells after surgery and that’s include the cases reclassified as invasive carcinoma. Conclusion: The results obtained in this analysis showing no axillary involvement will make us rethink the indications for the concomitant surgical approach of the breast and the axilla in cases with a diagnosis of DCIS as a way to reduce the axillary surgical overtreatment. It was not our goal to compare the costs and complications of each method of diagnosis and the prognostic factors after the treatment of DCIS. Citation Format: Andressa Amorim, Andre Mattar, Marcellus Ramos, Reginaldo Coelho Lopes, Luciana Damous, Luiz Henrique Gebrim. Ductal carcinoma in situ: An excess regard of the axilla? [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO5-03-02.

Abstract GS03-01: Magnetic Resonance Imaging and a 12-Gene Expression Assay to Optimize Local Therapy for Ductal Carcinoma In Situ: 5-year clinical outcomes of E4112

Abstract BACKGROUND. Advanced diagnostics such as magnetic resonance imaging (MRI) and gene-expression profiles are potentially useful to guide treatment in patients with ductal carcinoma in situ (DCIS). To evaluate these tests, we performed a prospective single arm multicenter study. We have previously reported the impact of MRI on surgical management of DCIS patients, and the effect of a 12-gene DCIS Score (DS) on radiotherapy (RT) use after wide local excision (WLE). We now report a pre-planned analysis of ipsilateral breast events (IBE) at 5-years. METHODS. Adult women with a core needle biopsy diagnosis of DCIS and eligible for WLE based on conventional imaging were registered following consent. All registered patients underwent breast MRI. Those still eligible, and willing, to receive WLE after appropriate follow-up biopsies underwent resection to free margins. DCIS sections were submitted to Exact Sciences for DS. Those with a low DS (< 39) were advised to omit RT; those with intermediate/high (inter/hi) DS (≥39) were advised to receive RT. All participants were monitored at 6-month intervals for any breast cancer event, and for survival. An IBE was defined as the first DCIS or invasive recurrence in the ipsilateral breast following the final WLE. Participants without IBE were censored by date of last contact or date of death for those who died. Follow-up was truncated at 5 years from WLE. Using data available as of 07-06-2023, Kaplan-Meier (K-M) curves were constructed to estimate the time-to-event distributions for subjects who received RT and for those who did not. The 5-year IBE rates and 95% confidence intervals (CIs) were estimated from K-M curves for all subjects with a DS (analogue of Intention to Treat [ITT] analysis), and for the subset who were compliant with their DS-based RT recommendation (Per Protocol analysis). The analyses were repeated for subgroups based on age at DCIS diagnosis (< 50 vs. ≥ 50). RESULTS. Of 339 women evaluable for the previously reported primary analysis (PMID 30653209), 171 (50.4%) underwent WLE with free surgical margins and had DS available for RT recommendations (ITT population). Of these, 7/82 low DS patients underwent RT, and 5/89 inter/hi DS patients declined RT; thus, the adherence to DS-based RT recommendations was 93%. At a median of 5 years of follow-up from final WLE, the ITT population experienced a total of eight IBE events (4.8%, 95% CI 2.4, 9.4) with 5-year IBE rates that were similar for participants with a low DS and for those with a inter/hi DS: 5.1% (95% CI: 1.9, 12.9) and 4.5% (95% CI 1.7, 11.7), respectively. Stratification by age did not alter these results: among women aged < 50 years (n=33), the IBE rate was 6.7% (95% CI 1.0, 38.7) for low DS and 5.6% (95% CI 0.8, 33.4) for inter/hi DS. Among women aged ≥ 50 years (n=138), the IBE rate was 4.7% (95% CI 1.5, 13.8) for low DS and 4.3% (95% CI 1.4, 12.7) for inter/hi DS. In the per-protocol analysis (N=159 adherent to RT recommendations), IBE rates were also similar for participants who had a low DS and no RT [5.5% (95% CI 2.1, 14.1)] and for those with inter/hi DS who received RT [4.8% (95% CI: 1.8% to 12.3%)]. Again, there was no discernible influence by age as categorized above. CONCLUSION. We report the first prospective data on use of DCIS Score for RT decisions, and 5-year IBE rates. We find that DS-based recommendations are followed by >90% of patients. Although the sample size is limited, the data are reassuring in that the IBE rate is similar between the low DS group treated with WLE alone and the inter/hi DS group treated with WLE and radiation, whereas prior studies have shown a marked difference in IBE rates by DS with excision alone. Therefore, this prospective trial provides strong evidence to support the omission of RT after surgery in DCIS patients with low DS, and its use in patients with intermediate/high DS. Citation Format: Seema Khan, Justin Romanoff, Constantine Gatsonis, Habib Rahbar, Ruth Carlos, Sunil Badve, Jean Wright, Constance Lehman, Worta McCaskill-Stevens, Ralph Corsetti, Derrick Spell, Kenneth Blankstein, Linda Han, Jennifer Sabol, John Bumberry, Ilana Gareen, Bradley Snyder, Lynne Wagner, Kathy Miller, Joseph Sparano, Christopher Comstock. Magnetic Resonance Imaging and a 12-Gene Expression Assay to Optimize Local Therapy for Ductal Carcinoma In Situ: 5-year clinical outcomes of E4112 [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr GS03-01.

Abstract PS01-10: Surgical margins in breast conserving surgery (BCS) for ductal carcinoma in-situ (DCIS) and clinical outcomes: significant associations with increased recurrence and overall survival

Abstract Background: Optimal surgical margin in breast conserving surgery (BCS) for DCIS are not established, largely due to an absence of accurate margin data. A margin width of 2mm was adopted by the American College of Surgeons (ACS). The UK Association of Breast Surgery (ABS) recommended a 1mm margin. Conducting a randomized controlled trial to answer this question is unfeasible; therefore we used retrospective histological margin data from available datasets to assess whether there is an association between margin width and time to recurrence (TTR). Methods: Patients were included if aged >18 years with a new diagnosis of DCIS alone, between 2003-2014, within UK NHS Breast Screening Programme (BSP). Primary treatment included BCS and a minimum histological excision margin width recorded. Exclusion criteria included: i) prior history of DCIS; ii) prior history of invasive cancer or its diagnosis within 3 months of initial surgical treatment for DCIS. Data was extracted from English Cancer Registries (CR), ABS and Sloane audits. TTR was defined as time from diagnosis to local or distant recurrence. Cox regression was used to compare TTR by surgical margin width utilising a range of thresholds, with focus on < 1mm vs ≥1mm; < 2mm vs ≥2mm and ≥1- < 2mm vs ≥2mm. Patients with 0mm margin or where categorized as “clear/not stated” were excluded from these analyses. Models were adjusted for age group, DCIS grade and size, ER status, number of BCSs, radiotherapy (RT) received, diagnosis year and CR centre. Overall survival (OS) was a secondary endpoint. Results: 17,260 patients diagnosed with DCIS having BCS as definitive surgery were identified between 2003-2014; 679 (5%), 2105 (15%), 1339 (10%) and 9744 (70%) with recorded margins of >0- < 1mm, ≥1- < 2mm, ≥2- < 3mm and ≥3mm, respectively. 10,253 (59%) patients received RT and in 7,007 (41%) RT receipt was unknown. Overall, 14,004 (81%), 3,052 (18%) and 201 (1%) patients had one, two and ≥3 BCSs respectively; there was no significant change in these percentages over time (p=0.2 Cuzick test). Median follow-up time for the cohort was 8.2 years (IQR: 6.1-11.2). 2221 (13%) patients had a subsequent event: 1741/2221 (78%) invasive recurrence and 480/2221 (22%) DCIS alone. The annual event rate over 15 years of follow-up was relatively consistent at 1.2% per annum (pa) for margins ≥2mm versus 1.8% pa for margins < 2mm. A shorter TTR was observed for patients with surgical margins < 1mm vs ≥1mm (adjusted HR=1.30; 95%CI: 1.05-1.62; p=0.02); < 2mm vs ≥2mm (adjusted HR=1.20; 95%CI: 1.06-1.36; p=0.004) and ≥1- < 2mm vs ≥2mm (adjusted HR=1.20; 95%CI: 1.04-1.40; p=0.02). Margins >2mm did not appear to significantly improve TTR (adjusted HR=0.96; 95%CI: 0.85-1.08; p=0.50 for ≥5mm vs ≥2- < 5mm). Models also showed that risk of recurrence increased as the number of BCSs increased (adjusted HR=1.25; 95%CI: 1.10-1.43: p< 0.001 for 2 vs 1 and adjusted HR=2.03; 95%CI: 1.36-3.03: p< 0.001 for 3+ vs 1). In total, 1552 (9%) patients had died. OS appeared reduced for patients with surgical margins < 2mm vs ≥2mm (adjusted HR=1.25 (1.07-1.45); p=0.005) and for ≥1- < 2mm vs ≥2mm (adjusted HR=1.28 (1.07-1.54); p=0.008). Margins <2mm did not appear to significantly improve OS further (adjusted HR=1.06; 95%CI: 0.92-1.21; p=0.43 for ≥5mm vs ≥2- < 5mm). Conclusion: Patients with DCIS with histological margins of < 2mm, adjusted for other clinical factors, have significantly worse TTR and OS rates compared to margins ≥2mm; the increased annual event rate is consistent out to 15 years. More than 1 BCS is also associated with an increased risk of recurrence. These findings are important for the treatment of patients with DCIS. Citation Format: John Robertson, D Mark Sibbering, Sikhuphukile Ndebele-Mahati, Olive Kearins, Sarah Pinder, Ashu Gandhi, Judith Bliss, Lucy Kilburn. Surgical margins in breast conserving surgery (BCS) for ductal carcinoma in-situ (DCIS) and clinical outcomes: significant associations with increased recurrence and overall survival [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PS01-10.

Abstract PO5-20-01: SENTINOT2- Use of superparamagnetic iron oxide tracer to avoid unnecessary sentinel lymph node biopsies

Abstract Background/Purpose: The use of superparamagnetic nanoparticles of iron oxide tracers (Magtrace) and electromagnetometers (SentiMag) for the detection of sentinel lymph nodes (SLN) during breast cancer surgery has been demonstrated to be noninferior to traditional radioisotope (RI) and blue dye detection, with additional safety benefits. Previous work has shown that transcutaneous detection of SLN with Magtrace/Sentimag is possible for over 30 days. Because of the safety, efficacy, and long detection window of Magtrace, we aim to investigate the use of Magtrace to prevent unnecessary SLN biopsies (SLNB) in breast cancer surgery. SLNB are commonly performed during breast conserving surgeries (BCS) or mastectomy for patients with a preoperative diagnosis of ductal carcinoma in-situ (DCIS). Because metastasis is not expected in patients diagnosed with DCIS, SLNB may be unnecessary and potentially harmful. However, in 15-25% of cases, unexpected invasive carcinoma is found during the post-surgical histopathological analysis of the resected breast tissue. For these cases, if SLNB are forgone during the initial surgery, SLNB during a second (delayed) procedure is the usual standard of care to evaluate SLN for metastasis. However, potential changes to lymphatic drainage following the initial resection may affect tracer localization to SLN. Consequently, we aim to compare SLN detection rates during delayed SLNB with Magtrace administered prior to initial BCS or mastectomy and subsequent RI tracer administered prior to delayed SLNB. Methods: SENTINOT2 is an ongoing international trial with BCM as the sole US site. For eligible patients with a preoperative diagnosis of DCIS, Magtrace will be administered prior to BCS or mastectomy. If invasive carcinoma is found from the post-surgical histopathological analysis, patients will receive delayed SLNB within 4 weeks of their initial surgery. Prior to delayed SLNB, patients will be randomized into two groups differing in the order of modality used for SLN detection (Magtrace or RI). Subjects with the following conditions will be excluded from the study: hypersensitivity to Magtrace, iron overload disease, pregnancy, and lactation. The total expected accrual for this study is 538 subjects globally and 50 subjects at BCM. Results: Currently, 19 patients have been enrolled in SENTINOT2. The subject population is 11% Asian, 26% Black/African American, and 47% Caucasian with non-Hispanic ethnicity. 5% of subjects identified as Hispanic Caucasian and 11% of subjects declined to report their race or ethnicity. 79% of patients had mastectomies, while 21% had BCS. After post-surgical histopathological analysis, 21% (4/19) patients were determined to have invasive carcinoma and received delayed SLNB. 50% (2/4) of these patients were randomized to have Magtrace as their first SLN detection modality (Mag-RI) while the other 50% (2/4) had RI as their first SLN detection modality (RI-Mag). Table 1 shows comparable SLN detection rates between Magtrace and RI for patients who received delayed SLNB. Only 1/4 patients showed SLN metastasis. For this patient, the positive SLN was successfully detected by both modalities. Conclusion: Magtrace has shown potential in delayed SLN detection and the use of Magtrace has prevented 79% (15/19) of enrolled patients from receiving unnecessary SLNB. Table 1. Number of Lymph Nodes (LN) Detected by Magtrace/Radioisotope, Biopsied and Positive for Metastasis Citation Format: Mary Bajomo, Ivan Marin, Jessica Montalvan, Margarita Riojas-Barrett, Logan Healy, Elizabeth Bonefas, Stacey Carter, Alastair Thompson. SENTINOT2- Use of superparamagnetic iron oxide tracer to avoid unnecessary sentinel lymph node biopsies [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO5-20-01.

Abstract PS03-07: Morphometric signature identifies ductal carcinoma in situ of the breast with low risk of progression to invasive breast cancer

Abstract Background. Ductal carcinoma in situ (DCIS) is a frequently found precursor of invasive breast cancer (IBC). However, the majority of DCIS will never progress to IBC. As we cannot distinguish yet which DCIS will remain indolent (‘harmless’) from those that might progress in the future to IBC, almost all women with DCIS are intensively treated by surgery, often followed by radiotherapy. This brings an urgent clinical need to learn distinguishing harmless from potentially progressive DCIS to save many women with indolent DCIS the burden of unnecessary overtreatment. Aim. We aimed to investigate if the geometry and spatial configuration of DCIS ducts in Hematoxylin-Eosin (H&E) stained tissue sections are related to the risk of progression of DCIS to ipsilateral IBC (iIBC). Methods. We obtained data from a population-based cohort of women diagnosed with primary DCIS between 1989 and 2004 in the Netherlands, treated with breast conserving surgery (BCS) only and a median follow-up time of 12 years. A nested case-control study (n=689) was designed in which patients diagnosed with iIBC recurrences during follow-up were considered as “cases” (n= 226) and those with no subsequent iIBC as “controls” (n=463). The DCIS and stroma regions were digitally annotated on H&E-stained whole slide images (WSIs) by a pathologist as ground truth for the deep learning neural network of HALO AI module (IndicaLabs). We developed a computational pipeline to automatically detect and measure stroma areas, DCIS ducts, and the nucleus of their cells. We validated the accuracy of DCIS detection in H&Es WSIs from an external study, in which DCIS regions were digitally annotated by an independent pathologist (Translational Breast Cancer Research Consortium, TBCRC). We classified cases and controls according to morphological measurements using logistic ridge regression with double-loop cross-validation, followed by hierarchical clustering. The risk of subsequent iIBC after primary DCIS diagnosis was evaluated by multivariate Cox proportional hazards models. Results. The accuracy of DCIS detection performed by the computational pipeline was compared with pathologist annotations in 20 slides from the TBCRC study. Results showed a satisfactory DCIS overlap area agreement of 0.76 (0.68 – 0.83). We applied the DCIS computational pipeline on the case-control series. We obtained 15 morphological measurements for each DCIS duct, such as duct area, cell density, distance between ducts, average nucleus area, etc. We calculated 8 distribution parameters from each measurement in each WSI, including median and range. After leaving out redundant variables, 55 unique morphometric variables were obtained, representing the heterogeneity of DCIS ducts per WSI. The c lassifier revealed a median area-under the curve (AUC) of 0.66 (0.55-0.77) to predict 5-years free of iIBC, 0.59 (0.50-0.67) to predict 10-years and 0.60 (0.52-0.68) to predict 15-years. The 30 variables with the highest association with outcome were used to build four morphometric signatures. Signature number 1, which is characterized by lesions with small-sized ducts, a lower number of cells and a lower DCIS/stroma area ratio, showed a significant lower risk of developing iIBC compared to the other three signatures in a multivariate Cox regression model including grade, ER, COX-2 and HER2 expression: HR = 0.56 (0.28-0.78 95%CI). Conclusion. We developed a computational pipeline able to detect and measure DCIS ducts in H&E WSIs with high accuracy and reproducibility. DCIS lesions presenting the morphometric signature of small-sized DCIS ducts have a very low chance to progress to invasive breast cancer. After successful validation, our morphometric method will serve as a robust and easy to implement biomarker for de-escalation strategies in DCIS, and as such, could limit unnecessary overtreatment in the near future. Citation Format: Marcelo Sobral-Leite, Simon Castillo, Shiva Vonk, Xenia Melillo, Noomie Lam, Brandi de Bruijn, Yeman Hagos, Joyce Sanders, Mathilde Almekinders, Lindy Visser, Emilie Groen, Carolien Van der Borden, Petra Kristel, Ercan Caner, Leyla Azarang, Yinyin Yuan, Renee Menezes, Esther Lips, Jelle Wesseling, Grand Challenge PRECISION Consortium. Morphometric signature identifies ductal carcinoma in situ of the breast with low risk of progression to invasive breast cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PS03-07.

Abstract 6255: Personalized medicine for DCIS

Abstract Background: In 2023, 55,720 women will be diagnosed with non-invasive ductal carcinoma in situ (DCIS) in the United States. We evaluated RNA sequencing (RNA-Seq), clinical and social factors that drive subsequent breast events in a DCIS study population enriched for Black women (30%). Methods: RNA was extracted from macrosections of archival formalin-fixed paraffin-embedded (FFPE) DCIS tissue from Resource Archival Human Breast Tissue (RAHBT) from the St. Louis Breast Tissue Registry at Washington University School of Medicine and the Dana Farber Cancer Institute patient cohorts. Tissues were prepared by microsection of 5 uM whole section from unstained slides (Fisher). RNA was extracted using Qiagen RNeasy FFPE Kits from macrosectioned DCIS specimens. Purified total RNA was evaluated for quality and quantity using the Agilent Fragment Analyzer RNA assay. Bulk RNA sequencing was piloted in DCIS case-control samples using the SMART-seq and Hybrid Capture platforms at the DFCI Molecular Biology Core Facilities. Raw reads were aligned to the GRCh38/hg38 reference genome using STAR. Preliminary quality control analysis of a curated gene list showed higher quality data using the Hybrid Capture technology. Libraries for Hybrid Capture were pooled in 8plex reactions and hybridized to Twist Exome 2.0 probes for target enrichment. The final library pools were sequenced on an Illumina NovaSeq. Cases were defined as women diagnosed with DCIS in 1999 or later with subsequent invasive breast cancer, local DCIS recurrence, or lobular CIS recurrence. Controls were defined as women diagnosed with DCIS in 1999 or later without subsequent breast events during a similar follow-up time. The R package DESeq2 was used for data analysis. Results: The mean age at DCIS diagnosis was 56.3 (Std Dev 10.23). The mean follow-up time was 147.8 months. Hybrid Capture RNA-Seq files are stored and analyzed from the Harvard Medical School O2 Cluster using R programming (version 4.2.2, DEGreport). Quality control analyses demonstrated that the majority of the samples sequenced by Hybrid Capture had over 20 million total reads. Principal Component Analyses (PCA) and hierarchical clustering analyses of 19,821 protein-coding genes were conducted on the 143 DCIS samples sequenced using Hybrid Capture. PC1 was race (9%). A significant association was observed for follow-up time (PC3, 4.03%). First, we explored the association of the candidate gene ERBB2. The mean transcript abundance for ERBB2 was 11784.37 (case-control p-value=0.08). Preliminary analysis of selected genes of interest did not show statistically significant differences between cases and controls after FDR p-value adjustment. Differential gene expression analyses are ongoing. Conclusion: This study demonstrates the feasibility of generating high-quality RNA-seq data from diverse, archival DCIS samples. Citation Format: Aditi Hazra. Personalized medicine for DCIS [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6255.

Surgical outcomes of total duct excision in the diagnosis and management of nipple discharge.

Total duct excision (TDE) is performed for the diagnosis and management of nipple discharge. The Association of Breast Surgery's recent guidelines recommend considering diagnostic surgery for single-duct, blood-stained or clear nipple discharge, and for symptomatic management. We retrospectively reviewed the diagnostic and surgical outcomes of all cases of TDE between January 2013 and November 2019. In total, 259 TDEs were carried out: 219 for nipple discharge, 29 for recurrent mastitis, 3 for screening abnormalities and 8 for breast lumps. Of the nipple discharge group, 121 had blood-stained discharge. Mean patient age was 52 years (range 19-81). Median follow-up time was 45 months (interquartile range 24-63). The following cases were identified on histopathology: 236 benign breast changes, 10 atypical ductal hyperplasia, 4 lobular carcinoma in situ, 2 low-grade ductal carcinoma in situ (DCIS), 3 intermediate-grade DCIS, 2 high-grade DCIS and 2 invasive ductal carcinomas. In total, 3.5% of patients who underwent TDE had a diagnosis of DCIS or invasive carcinoma. Blood-stained discharge was associated with a significant increase in risk of DCIS or carcinoma compared with other nipple discharge colours (p = 0.043). The most common complications of TDE were infection, poor wound healing and haematoma. Nipple discharge recurred in 14.2% of cases. TDE can be considered for the diagnostics and management of nipple discharge. Blood-stained nipple discharge increases the risk of DCIS or malignancy, but the majority of the time TDE reveals benign breast pathology.

Evolving Treatment Paradigms for Low-Risk Ductal Carcinoma In Situ: Imaging Needs.

Ductal carcinoma in situ (DCIS) is a nonobligate precursor to invasive cancer that classically presents as asymptomatic calcifications on screening mammography. The increase in DCIS diagnoses with organized screening programs has raised concerns about overdiagnosis, while a patientcentric push for more personalized care has increased awareness about DCIS overtreatment. The standard of care for most new DCIS diagnoses is surgical excision, but nonsurgical management via active monitoring is gaining attention, and multiple clinical trials are ongoing. Imaging, along with demographic and pathologic information, is a critical component of active monitoring efforts. Commonly used imaging modalities including mammography, ultrasound, and MRI, as well as newer modalities such as contrast-enhanced mammography and dedicated breast PET, can provide prognostic information to risk stratify patients for DCIS active monitoring eligibility. Furthermore, radiologists will be responsible for closely surveilling patients on active monitoring and identifying if invasive progression occurs. Active monitoring is a paradigm shift for DCIS care, but the success or failure will rely heavily on the interpretations and guidance of radiologists.

Surgical De-Escalation for Re-Excision in Patients with a Margin Less Than 2 mm and a Diagnosis of DCIS.

The current surgical guidelines recommend an optimal margin width of 2 mm for the management of patients diagnosed with ductal carcinoma in situ (DCIS). However, there are still many controversies regarding re-excision when the optimal margin criteria are not met in the first resection. The purpose of this study is to understand the importance of surgical margin width, re-excision, and treatments to avoid additional surgery on locoregional recurrence (LRR). The study is retrospective and analyzed surgical margins, adjuvant treatments, re-excision, and LRR in patients with DCIS who underwent breast-conserving surgery (BCS). A total of 197 patients were enrolled. Re-operation for a close margin rate was 13.5%, and the 3-year recurrence was 7.6%. No difference in the LRR was reported among the patients subjected to BCS regardless of the margin width (p = 0.295). The recurrence rate according to margin status was not significant (p = 0.484). Approximately 36.9% (n: 79) patients had resection margins < 2 mm. A sub-analysis of patients with margins < 2 mm showed no difference in the recurrence between the patients treated with a second surgery and those treated with radiation (p = 0.091). The recurrence rate according to margin status in patients with margins < 2 mm was not significant (p = 0.161). The margin was not a predictive factor of LRR p = 0.999. Surgical re-excision should be avoided in patients with a focally positive margin and no evidence of the disease at post-surgical imaging.

Mode of Detection of Second Breast Cancers in Patients Undergoing Surveillance After Treatment of Ductal Carcinoma in Situ.

For patients undergoing posttreatment surveillance after ductal carcinoma in situ (DCIS), the NCCN Guidelines for Breast Cancer recommend annual breast imaging and physical examination every 6 to 12 months for 5 years, and then annually. The aim of our study was to evaluate the modes of detection (imaging, patient reported, or physical examination) of second cancers in a cohort of patients undergoing surveillance after primary DCIS treatment to better inform surveillance recommendations. We performed a retrospective cohort study of patients with DCIS treated between January 1, 2008, and December 31, 2011, within a large integrated health care system. Information on patient demographics, index DCIS treatment, tumor characteristics, and mode of detection of second breast cancer was obtained from the electronic health record or chart review. Our study cohort consisted of 1,550 women, with a median age of 59 years at diagnosis. Surgical treatment of DCIS included lumpectomy (75.0%; n=1,162), unilateral mastectomy (21.1%; n=327), or bilateral mastectomy (3.9%; n=61), with or without sentinel lymph node biopsy. Additionally, 44.4% (n=688) and 28.3% (n=438) received radiation and endocrine therapies, respectively. Median follow-up was 10 years, during which 179 (11.5%) women were diagnosed with a second breast cancer. Of the second cancers, 43.0% (n=77) were ipsilateral and 54.8% (n=98) contralateral, and 2.2% (n=4) presented with distant metastases; 61.5% (n=110) were invasive, 36.3% (n=65) were DCIS, and 2.2% (n=4) were Paget's disease. Second breast cancers were imaging-detected in 74.3% (n=133) of cases, patient-detected in 20.1% (n=36), physician-detected in 2.2% (n=4), and detected incidentally on imaging or pathology from procedures unrelated to oncologic care in 3.4% (n=6). In our cohort of patients undergoing surveillance following diagnosis and treatment of DCIS, 2% of second breast cancers were detected by a clinical breast examination. This suggests that survivorship care should prioritize mammography and patient education regarding breast self-examination and symptoms that warrant evaluation to detect second breast cancers.

Could breast multiparametric MRI discriminate between pure ductal carcinoma in situ and microinvasive carcinoma?

Ductal carcinoma in situ (DCIS) is often reclassified as invasive cancer in the final pathology report of the surgical specimen. It is of significant clinical relevance to acknowledge the possibility of underestimating invasive disease when utilizing preoperative biopsies for a DCIS diagnosis. In cases where such histologic upgrades occur, it is imperative to consider them in the preoperative planning process, including the potential inclusion of sentinel lymph node biopsy due to the risk of axillary lymph node metastasis. To assess the capability of breast multiparametric magnetic resonance imaging (MP-MRI) in differentiating between pure DCIS and microinvasive carcinoma (MIC). Between January 2018 and November 2022, this retrospective study enrolled patients with biopsy-proven DCIS who had undergone preoperative breast MP-MRI. We assessed various MP-MRI features, including size, morphology, margins, internal enhancement pattern, extent of disease, presence of peritumoral edema, time-intensity curve value, diffusion restriction, and ADC value. Subsequently, a logistic regression analysis was conducted to explore the association of these features with the pathological outcome. Of 129 patients with biopsy-proven DCIS, 36 had foci of micro-infiltration on surgical specimens and eight were diagnosed with invasive ductal carcinoma (IDC). The presence of micro-infiltration foci was significantly associated with several MP-MRI features, including tumor size (P <0.001), clustered ring enhancement (P <0.001), segmental distribution (P <0.001), diffusion restriction (P = 0.005), and ADC values <1.3 × 10-3 mm2/s (P = 0.004). Breast MP-MRI has the potential to predict the presence of micro-infiltration foci in biopsy-proven DCIS and may serve as a valuable tool for guiding therapeutic planning.

Survival Outcomes Based on Axillary Surgery in Ductal Carcinoma In Situ: A Nationwide Study From the Korean Breast Cancer Society.

In total mastectomy (TM), sentinel lymph node biopsy (SLNB) is recommended but can be omitted for breast-conserving surgery (BCS) in patients with ductal carcinoma in situ (DCIS). However, concerns regarding SLNB-related complications and their impact on quality of life exist. Consequently, further research is required to evaluate the role of axillary surgeries, including SLNB, in the treatment of TM. We aimed to explore the clinicopathological factors and outcomes associated with axillary surgery in patients with a final diagnosis of pure DCIS who underwent BCS or TM. We retrospectively analyzed large-scale data from the Korean Breast Cancer Society registration database, highlighting on patients diagnosed with pure DCIS who underwent surgery and were categorized into two groups: BCS and TM. Patients were further categorized into surgery and non-surgery groups according to their axillary surgery status. The analysis compared clinicopathological factors and outcomes according to axillary surgery status between the BCS and TM groups. Among 18,196 patients who underwent surgery for DCIS between 1981 and 2022, 11,872 underwent BCS and 6,324 underwent TM. Both groups leaned towards axillary surgery more frequently for large tumors. In the BCS group, clinical lymph node status was associated with axillary surgery (odds ratio, 11.101; p = 0.003). However, in the TM group, no significant differences in these factors were observed. Survival rates did not vary between groups according to axillary surgery performance. The decision to perform axillary surgery in patients with a final diagnosis of pure DCIS does not affect the prognosis, regardless of the breast surgical method. Furthermore, regardless of the breast surgical method, axillary surgery, including SLNB, should be considered for high-risk patients, such as those with large tumors. This may reduce unnecessary axillary surgery and enhance the patients' quality of life.

Radiology for Ductal Carcinoma In Situ of the Breast: Updates on Invasive Cancer Progression and Active Monitoring.

Ductal carcinoma in situ (DCIS) accounts for approximately 30% of new breast cancer diagnoses. However, our understanding of how normal breast tissue evolves into DCIS and invasive cancers remains insufficient. Further, conclusions regarding the mechanisms of disease progression in terms of histopathology, genetics, and radiology are often conflicting and have implications for treatment planning. Moreover, the increase in DCIS diagnoses since the adoption of organized breast cancer screening programs has raised concerns about overdiagnosis and subsequent overtreatment. Active monitoring, a nonsurgical management strategy for DCIS, avoids surgery in favor of close imaging follow-up to de-escalate therapy and provides more treatment options. However, the two major challenges in active monitoring are identifying occult invasive cancer and patients at risk of invasive cancer progression. Subsequently, four prospective active monitoring trials are ongoing to determine the feasibility of active monitoring and refine the patient eligibility criteria and follow-up intervals. Radiologists play a major role in determining eligibility for active monitoring and reviewing surveillance images for disease progression. Trial results published over the next few years would support a new era of multidisciplinary DCIS care.

Evaluation of the Influence of Geodimensional and Histological Parameters on the Need for Margin Widening in Breast Lesions Marked With Magnetic Seeds.

Breast cancer is an important topic worldwide, posing morbidity and mortality to women. Considerable efforts have been put in the early recognition of malignancy through different screening methods, such as mammography and ultrasound. The precise localization of infraclinical malignant lesions is key in surgical management and magnetic seeds gather particular interest for this purpose. As with other systems, a need for reintervention may be needed to obtain adequate surgical margins. This work evaluated the relation between the need for surgical reintervention in order to obtain negative margins and geodimensional and histological parameters. The main objective was the identification of parameters significantly associated with reintervention for margin widening. A retrospective analysis of 198 patients from a single centre was performed. The association between pre-defined geodimensional and histological parameters and the need for margin widening in infraclinical lesions marked with magnetic seed was evaluated. Results showed that reintervention to widen margins was significantly higher in patients with ductal carcinoma in situ (DCIS) in the pre-operative biopsy when compared with invasive carcinoma (p = 0.03) in the bivariate analysis. No statistically significant differences were observed between the need for reintervention and lesion size (p = 0.197), breast quadrant location (p = 0.626) and distance of skin to lesion (p = 0.356). This work suggests that a more invasive margin clearance in lesions with a pre-operative DCIS diagnosis might obviate the need for reintervention to obtain negative margins. On the other hand, it is not necessary to be surgically more invasive in larger lesions, deeply located or that are present in a certain quadrant, since there are no significant differences regarding the need for reintervention.

Nationwide Analysis of Locoregional Management for Ductal Carcinoma In Situ in Males: An NCDB Analysis of the Surgical Approach to DCIS in Males.

Limited data exist regarding the optimal locoregional approach for males with ductal carcinoma in situ (DCIS). This study examined trends in management and survival for males with DCIS. The National Cancer Database (NCDB) was queried for males with a diagnosis of DCIS from 2006 to 2017. Patients were categorized by locoregional management. Continuous variables were evaluated by Kruskal-Wallis and categorical variables by chi-square or Fisher's exact test. Univariable and multivariable logistic regressions were performed to evaluate for predictors of patients receiving partial mastectomy (PM) with radiation. Survival was analyzed by Kaplan-Meier. Between 2006 and 2017, 711 males with DCIS were identified. Most received mastectomy alone (57.1%). No change was observed in management approach from 2006 to 2017. Patients who underwent mastectomy alone were mostly hormone-positive (95.9% were estrogen-positive, 90.9% were progesterone-positive), although this cohort was least likely to receive hormone therapy (17.2%). Among those who underwent PM with radiation, only 61% of those who were hormone-positive received hormone therapy. Univariable analysis demonstrated that those of black race had lower odds of receiving PM with radiation (odds ratio [OR], 0.58; 95% confidence interval [CI], 0.36-0.84), which persisted in the multivariable analysis with control for age and tumor size (OR, 0.32; 95% CI, 0.15-0.67). Overall survival did not differ significantly between the four treatment methods (p = 0.08). The management approach to male DCIS did not change from 2006 to 2017. Survival did not differ between treatment methods. Demographic and clinicopathologic features, including race, may influence locoregional treatments received, and further studies are needed to further understand this.

The effects of contemporary treatment of DCIS on the risk of developing an ipsilateral invasive Breast cancer (iIBC) in the Dutch population

PurposeTo assess the effects of contemporary treatment of ductal carcinoma in situ (DCIS) on the risk of developing an ipsilateral invasive breast cancer (iIBC) in the Dutch female population.MethodsClinical data was obtained from the Netherlands Cancer Registry (NCR), a nationwide registry of all primary malignancies in the Netherlands integrated with the data from PALGA, the Dutch nationwide network and registry of histo- and cytopathology in the Netherlands, on all women in the Netherlands treated for primary DCIS from 2005 to 2015, resulting in a population-based cohort of 14.419 women. Cumulative iIBC incidence was assessed and associations of DCIS treatment type with subsequent iIBC risk were evaluated by multivariable Cox regression analyses.ResultsTen years after DCIS diagnosis, the cumulative incidence of iIBC was 3.1% (95% CI: 2.6–3.5%) in patients treated by breast conserving surgery (BCS) plus radiotherapy (RT), 7.1% (95% CI: 5.5–9.1) in patients treated by BCS alone, and 1.6% (95% CI: 1.3–2.1) in patients treated by mastectomy. BCS was associated with a significantly higher risk for iIBC compared to BCS + RT during the first 5 years after treatment (HR 2.80, 95% CI: 1.91–4.10%). After 5 years of follow-up, the iIBC risk declined in the BCS alone group but remained higher than the iIBC risk in the BCS + RT group (HR 1.73, 95% CI: 1.15–2.61).ConclusionsAlthough absolute risks of iIBC were low in patients treated for DCIS with either BCS or BCS + RT, risks remained higher in the BCS alone group compared to patients treated with BCS + RT for at least 10 years after DCIS diagnosis.

Endocrine therapy initiation among women diagnosed with ductal carcinoma in situ breast cancer from 2001-2016.

487 Background: Endocrine therapy (ET) initiation in people within 1 year of diagnosis of estrogen-receptor-positive (ER+) ductal carcinoma in situ (DCIS) has ranged from 21-45% in prior studies; however, these studies did not evaluate initiation post-2011 and may not reflect current patterns of use. ET use following ER+ DCIS diagnosis can reduce the relative risks of recurrence and contralateral breast cancer by 30-50%. We evaluated ET initiation over time and by demographic, tumor, and treatment characteristics in the Kaiser Permanente Breast Cancer Survivors Study between 2001-2016. Methods: We included people aged 20+ years diagnosed with unilateral DCIS with at least 1 year of cancer-free follow-up from three U.S. integrated health systems. We excluded people with ER-negative disease, no surgery, and those who received chemotherapy or unknown radiation therapy. ET dispensings (tamoxifen and aromatase inhibitors) were extracted from electronic pharmacy records within 1 year of a person’s initial DCIS breast cancer diagnosis. Using generalized linear models with a log link and Poisson distribution, we estimated relative rates (RRs) of ET use (vs none) over time and by demographic, tumor, and other treatment characteristics. Results: Among 1,782 pre- and postmenopausal people, 577 (32%) initiated ET within 1 year of diagnosis. From 2001-2016, ET use did not change over time (34% vs 36%), tamoxifen use declined slightly (34% vs 29%), and aromatase inhibitor use increased slightly (0% vs 7%). People were less likely to initiate ET if they were ≥65 years, Black, had borderline or unknown ER status, were not tested for ER, had breast conserving surgery (BCS) without radiation, or had a unilateral mastectomy. Conclusions: Only one-third of people with DCIS diagnosed in a community healthcare setting and potentially eligible for ET, initiated treatment within 1 year of their diagnosis. Previous studies have shown long-term benefits of ET use in people with DCIS; however, we saw no increase in use over time. Concerns about side-effects, overdiagnosis and overtreatment of DCIS, and confusion about treatment guidelines may explain relatively low ET initiation.[Table: see text]