The mechanisms of action and targeting potential of vasculogenic mimicry in breast cancer metastasis

ABC 1 (1st International consensus guidelines for advanced breast cancer): A positive step

Glycyrrhetinic acid suppresses breast cancer metastasis by inhibiting M2-like macrophage polarization via activating JNK1/2 signaling

e13121 Background: Metastatic breast cancer remains a major clinical challenge, characterized by poor prognosis and limited therapeutic options. The incidence of metastatic female breast cancer increased from 5.8 to 7.9 per 100,000 females from 2001 to 2021. The Hippo pathway effector YAP1 plays a critical role in driving tumor growth and metastasis in many cancers including breast but little is known about the gene-specific changes that occur when breast cancers have metastasized. This study aimed to investigate the extent of genomic alterations, including copy number alterations (CNAs) and mutations, in YAP1 and its downstream genes in metastatic breast cancer compared to nonmetastatic breast cancer. Methods: Genomic data for the YAP1 gene and its downstream target genes (CTGF, Cyr61, MCL-1, TOP2A, FOSL2, and ANKRD1) were obtained from cBioPortal. This included mutation data and CNA data, considering both amplifications and deletions as CNA events. The chi-square test was performed using GraphPad Prism 10 to compare the frequencies of mutations and CNAs between metastatic and non-metastatic breast cancer cases. Results: A total of 2390 samples of metastatic breast cancer and 9289 samples of non-metastatic breast cancer were analyzed for mutations. Among them, a significantly higher percentage of mutations in the YAP1 (P ≤ 0.0001), ANKRD1 (P ≤ 0.0001), MCL-1 (P ≤ 0.0001), and TOP2A (P ≤ 0.0001) genes was observed in metastatic breast cancer compared to non-metastatic breast cancer. Evaluating CNAs in 2197 cases in the metastatic breast cancer group compared to 9289 cases in the non-metastatic breast cancer group demonstrated a significantly higher frequency of CNAs in the YAP1 ( P ≤ 0.0001), Cyr61 (P ≤ 0.0001), CTGF ( P ≤ 0.0001), ANKRD1 ( P ≤ 0.0001), TOP2A (P ≤ 0.0001) and FOSL2 (P ≤ 0.0001) genes among metastatic breast cancer. Conclusions: This study revealed significant genomic alterations in the YAP1 gene and its downstream genes in metastatic breast cancer. These findings highlight the importance of the YAP1 pathway in breast cancer metastasis and suggest that targeting this pathway may have therapeutic potential for primary and metastatic breast cancer. Frequency of mutations and copy number alterations (CNAs) in metastatic vs. non-metastatic breast cancer. Gene Metastatic Breast Cancer Mutation Frequency (%) Non-Metastatic Breast Cancer Mutation Frequency (%) P-value Metastatic Breast Cancer CNA Frequency (%) Non-Metastatic Breast Cancer CNA Frequency (%) P-value YAP1 0.75 0.17 <0.0001 5.1 1.18 <0.0001 CTGF 0.13 0.18 0.781 5.42 0.65 <0.0001 Cyr61 0.17 0.16 0.999 3.9 0.65 <0.0001 MCL-1 0.63 0.11 <0.0001 10.74 11.93 0.121 ANKRD1 1.17 0.09 <0.0001 1.96 0.25 <0.0001 TOP2A 0.96 0.18 <0.0001 8.06 3.6 <0.0001 FOSL2 0.17 0.1 0.317 3.64 0.62 <0.0001

Background Endocrine therapies and CDK4/6 inhibitors have dramatically improved outcomes for patients with hormone receptor-positive (HR+) metastatic breast cancer (MBC). To help inform treatment decisions among healthcare providers (HCPs) caring for patients with MBC, we have developed and regularly updated an online treatment decision support tool that provides recommendations from multiple breast cancer experts for specifically defined patient scenarios. Here we report data for HR+/HER2- MBC cases entered into the tool since 2016, capturing self-reported practice trends from HCPs compared with matched treatment recommendations from experts. Methods For the most recent MBC treatment tool (published October 2018), 5 breast cancer experts provided treatment consultation for 549 unique MBC case scenarios based on a simplified set of variables: disease phenotype, previous systemic therapy, visceral crisis (yes/no), rate of disease progression, and the presence or absence of germline BRCA1/2 mutations. HCPs used selection menus to enter patient and disease factors based on these variables along with their intended treatment plan. When completed, the experts’ treatment recommendations for that specific patient case were shown to the HCPs at which time they were asked to indicate if the expert recommendations changed their planned treatment. Results From October 2018 through June 2019, 603 HCPs entered 1127 patient case scenarios, including 581 HR+/HER2- MBC cases, in the most recent online tool. A comparison of expert and HCP treatment choices for select HR+/HER2- MBC case scenarios from the October 2016 and October 2018 tool is shown in the Table. In the setting of HR+/HER2- MBC, among those HCPs whose planned treatment differed from the consensus expert recommendation, 55% indicated that they would change their original choice of treatment. Conclusions CDK4/6 inhibitors have had a large impact on expert treatment recommendations for patients with HR+/HER2- MBC. However, data from this online treatment decision support tool suggest ongoing differences in practice between experts and community HCPs in this setting. For many cases entered into the tool, the practice of the majority of HCPs differed from expert consensus (Table). Consensus expert recommendations in this online tool changed the intended treatment plan of many using it and, therefore, can help optimize the care of patients with MBC. A detailed analysis of overall community practice trends for HR+/HER2- MBC along with a comparison of expert and HCP practice for different case scenarios will be presented. HR+/HER2- MBC Case Scenarios (no visceral crisis)Expert Consensus Recommendation (%)Expert Consensus Recommendation (%)HCP Practice Matched Expert Consensus Recommendation, % (n)HCP Practice Matched Expert Consensus Recommendation, % (n)2016201820162018de novoCDK4/6i + AI (100)CDK4/6i + AI (100)23 (111)32 (188)Previous (neo)adjuvant AICDK4/6i + FULV (92)CDK4/6i + FULV (90)22 (54)17 (77)Previous CDK4/6i + AIFULV (82)FULV ± EVE (92)0 (14)18 (40)Previous AI and CDK4/6i + FulvEVE + EXE (87)EVE + EXE (73)63 (19)28 (18) Citation Format: Timothy Quill, Sara Hurvitz, Kathy D. Miller, Ruth O'Regan, Tiffany A. Traina, Rachael Andrie, Kevin L. Obholz, Mohammad Jahanzeb. Treatment patterns for metastatic hormone receptor-positive breast cancer: Comparing expert and community practice [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P4-14-07.

Background: The distinction of primary lung cancer from metastatic breast cancer is crucial in patients presenting with a solitary pulmonary nodule after breast surgery. However definitive diagnosis of these nodules is often difficult due to similar radiological and pathological features in primary lung and metastatic breast cancer nodules. We assessed the feasibility of our diagnostic approach for these nodules by morphopathological and immunohistochemical examination, and estimated the frequency of primary lung cancer occurrence in breast cancer patients. Material and Methods: We evaluated solitary pulmonary nodules appearing in 24 patients (0.62% : 24/3851) after breast surgery between 1994 and 2006. Patients with metastases to organs other than lungs were not included. For histological examination, CT-guided core needle biopsy (CT-CNB), trans-bronchial lung biopsy (TBLB), or surgical resection was performed. Besides conventional morphopathological examination using HE staining, differential diagnosis was performed by immunohistochemical examination (thyroid transcription factor-1: TTF-1, surfactant pro-protein B: SPPB, estrogen receptor: ER, mammaglobin1: MGB1). The immunopositive results for TTF-1 and SPPB support the specimen diagnosis of primary lung cancer. The immunopositive and immunonegative results for ER and both TTF-1 and SPPB, respectively, suggest that the specimen has a high probability of being metastatic breast cancer. And for cases in which differential diagnosis failed in the morpopathological and TTF-1, SPPB, and ER examination, MGB1 examination was conducted. Several patient and tumor characteristics were evaluated according to the definitive diagnosis of pulmonary nodules in both metastatic breast and primary lung cancer groups, which were then compared using Student's t-test. Results: Biopsy specimens were obtained using minimally invasive methods (CT-CNB and TBLB) in 21 patients (87.5%). Surgical resection was performed for diagnosis and treatment in three patients. Differential diagnosis was obtained by morphopathological methods alone in 18 patients (75.0%, primary lung cancer: 6 cases, metastaic breast cancer: 12 cases) and by immunohistochemical examination in the remaining 6 (25.0%, primary lung cancer: 1 case, metastaic breast cancer: 5 cases). Final diagnosis was metastatic breast and primary lung cancer in 17 (70. 8%) and 7 patients (29.2%), respectively. The mean age was significantly higher in the primary lung than metastatic breast cancer patients group (67 years vs. 57 years: p=0.036). No significant difference in the average diameter of pulmonary nodules was observed between metastatic breast and primary lung cancer patients (2.32cm vs. 2.29 cm). Furthermore, there were no clinical findings between metastatic breast cancer patients group and primary lung cancer group. Conclusions: Our results show the clinical feasibility of our approach to the differential diagnosis of breast cancer relapse and primary lung cancer presenting as a solitary nodule in patients after breast surgery. Further, replication of our findings under independent setting is recommended. Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P6-03-05.

Discovery and development of novel therapies in advanced breast cancer: rapid development of ribociclib

Background Alterations in the MAPK pathway are known mechanisms for tumorigenesis in multiple solid tumors. While not major drivers in early breast cancers, activating MAPK pathway alterations have been invoked as potential resistance mechanisms in advanced hormone receptor positive (HR+) breast cancer. While MAPK pathway mutations are believed to be relatively rare in breast cancer, the accessibility of cell-free DNA (cfDNA) analysis allows for evaluation of their prevalence, co-occurring mutations, and associated clinical outcomes. In this study, we evaluated the incidence of MAPK pathway alterations and impact on clinical outcomes among patients with metastatic breast cancer (MBC). Methods Plasma was collected in patients with HR+ MBC at the Massachusetts General Hospital and Washington University in St. Louis, and cfDNA was analyzed via the Guardant 360 assay, a 74-gene next generation sequencing panel. The impact of MAPK pathway alterations on progression-free survival (PFS) and overall survival (OS) was analyzed using multivariable Cox regression analysis, adjusting for age, number of prior therapies, visceral metastases, de novo metastases, and PIK3CA alterations. PFS and OS were evaluated in the overall study population, as well as in subgroups that received endocrine therapy + CDK4/6 inhibitor, endocrine monotherapy and chemotherapy. Results Out of 647 HR+ MBC patients, 103 (16%) had non-synonymous mutations in the MAPK pathway detected in cfDNA. Median age was similar (61.9 and 60.7) in MAPK-altered and non-altered patients, respectively. Both groups had received a median of 2 prior lines of therapy (p=0.08). MAPK pathway alterations included NF1 (n = 45, 7.0%), KRAS (n = 22, 3.4%), BRAF (n = 22, 3.4%), MAPK1 (n = 8, 1.2%), MAP2K1 (n = 6, 0.9%), NRAS (n = 5, 0.8%), RAF1 (n = 5, 0.8%), HRAS (n = 4, 0.6%), ARAF (n = 4, 0.6%), MAP2K2 (n = 4, 0.6%), RIT1 (n = 3, 0.5%), and MAPK3 (n = 2, 0.3%). Mutant allele fractions ranged from 0.03 to 26. Co-alterations in PIK3CA occurred in 49% (n = 51), TP53 in 41% (n = 42), and ESR1 in 27% (n = 28). In multivariable analysis, patients with MAPK-altered HR+ MBC had significantly poorer median PFS, 7.6 months vs 11.5 months (HR: 1.6; p = 0.005; 95% CI: 1.2-2.2). There was no statistically significant impact on outcomes when stratifying by treatment type. Conclusions MAPK pathway alterations are associated with a significantly poorer PFS among patients with HR+ MBC. Further research is needed to independently validate these observations and evaluate the impact of genotype-directed therapy targeting MAPK-altered, HR+ MBC. Citation Format: Arielle J. Medford, Andrzej Niemierko, Whitney L. Hensing, Andrew A. Davis, Katherine Clifton, Jennifer C. Keenan, Lesli Kiedrowski, Ami N. Shah, Lorenzo Gerratana, Massimo Cristofanilli, Aditya Bardia. Cell-free DNA detection of alterations in the MAPK pathway in metastatic hormone receptor positive breast cancer: A multi-institutional analysis of incidence and clinical outcomes [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6744.

Advanced breast cancer (BC) is associated with heavier treatments and poorer prognosis than early BC. Despite mammographic screening, advanced BC incidence remains stable. Little is known about risk factors differentially associated with advanced BC. We analyzed factors predicting for postmenopausal advanced vs. early BC in the E3N cohort. E3N has been prospectively following 98,995 French women aged 50-65 years at baseline since 1990. Hazard ratios (HRs) and 95% confidence intervals (CIs) for advanced and early invasive BC were estimated with multivariate Cox competing risk hazard models. With a median follow-up of 15.7 years, 4,941 postmenopausal BC were diagnosed, including 1,878 (38%) advanced BC. Compared to early BC, advanced BC was differentially associated with excess weight (HR 1.39 [95% CI = 1.26-1.53] vs. 1.08 [95% CI = 1.00-1.17], phomogeneity < 0.0001) and living in a rural area (HR 1.14 [95% CI = 1.00-1.31] vs. 0.93 [95% CI = 0.82-1.04], phomogeneity 0.02). Excess weight was the only differential risk factor for advanced BC for hormone-dependent BC and for women compliant with screening recommendations. Previous mammography was associated with reduced advanced BC risk (HR 0.86 [95% CI = 0.73-1.00]) and increased early BC risk (HR 1.36 [95% CI = 1.18-1.56], phomogeneity < 0.0001), but only for hormone-dependent BC. Excess weight appears to be mostly associated with advanced BC, especially hormone-dependent BC. These results add to the evidence for maintaining weight within the recommended limits.

Introduction: Sacituzumab govitecan (SG) is FDA-approved for the treatment of both metastatic triple negative breast cancer (mTNBC) and hormone receptor positive (HR+)/HER2- metastatic breast cancer (MBC). In phase III clinical trials, SG caused grade 3 neutropenia in ∼50% of patients. However, the real-world incidence of SG-induced neutropenia and the practice patterns regarding the use of adjuvant growth factor use are not well characterized. Methods: In this single retrospective cohort study, we identified patients with HR+/HER2- or TNBC MBC who received SG between 2020-2024 per standard of care. We used manual review of electronic health records to identify key clinical characteristics, treatment history, safety parameters, and documented use of growth factor support via granulocyte colony stimulating factor (GCSF, either filgrastim or pegfilgrastim) while on treatment with SG. Results: We identified 74 patients with MBC who were treated with SG, including 45 patients with mTNBC (60.8%), 27 patients with HR+/HER2- MBC (36.5%), and 2 patients with heterogenous expression who were categorized as HR+/HER2+ MBC (2.7%). Median age was 56.5 years (range 28.4 - 81.1 years). Patients with mTNBC received a median of 2 prior lines of chemotherapy (range 0-5) and patients with HR+/HER2- disease received a median of 8 lines of prior therapy including 4 prior lines of chemotherapy (range 2-14 total lines, 0-8 lines of chemotherapy). Median time on SG was 4.4 months (range 0.26-39.8 months) for patients with mTNBC and 1.9 months (range 0.26-15.6 months) for patients with HR+/HER2- MBC. Most patients experienced any grade neutropenia while on SG (n=60, 81.1%), including most patients with mTNBC (n=37, 82.2%) and HR+/HER2- MBC (n=21, 77.8%). Grade 3 neutropenia was common during SG (n=39, 52.7%), with similar rates among patients with mTNBC (n=25, 55.6%) and HR+/HER2- MBC (n=12, 44.4%). Rates of neutropenic fever were low: in total 5/74 (6.8%), of whom 4/45 (8.9%) were mTNBC. A total of 8/74 (10.8%) patients were hospitalized for SG-related neutropenia with median length of stay 3.5 (range 1-10) days. Dose delays for any reason occurred in patients with mTNBC (n=18, 40.0%) and HR+/HER2- MBC (n=8, 29.6%), about half of which were due to neutropenia (for mTNBC n=7, 15.6%, HR+/HER2- MBC n=4, 14.8%). Dose reductions for any reason were also common among patients with mTNBC (n=21, 46.7%) and HR+/HER2- MBC (n=18, 66.7%), including some due to neutropenia (for mTNBC n=7, 15.6%, for HR+/HER2- n=4, 14.8%). Most patients discontinued SG due to disease progression for both mTNBC (n=43, 95.6%) and HR+/HER2- MBC (n=24, 88.9%). Two patients with HR+/HER2- MBC (7.4%) discontinued therapy due to toxicity. The remaining patients are still on therapy or discontinued for unrelated reasons. Most patients received GCSF during treatment with SG (n=64, 86.5%), most of whom received filgrastim (n=62, 83.8%) and a minority of whom received peg-filgrastim (n=7, 9.5%). In total 34/74 (45.9%) patients received primary GCSF prophylaxis and 24/74 (32.4%) patients received secondary GCSF prophylaxis. Rates of primary and secondary prophylaxis varied by subtype for mTNBC and HR+/HER2- respectively (primary: 37.8% and 55.6%; secondary: 40.0% and 22.2% respectively). Conclusion: In this single center retrospective study, &amp;gt;80% patients with mTNBC and HR+/HER2- MBC on SG experienced any grade neutropenia. Similar to published trials, nearly half of patients in both subgroups experienced grade 3 neutropenia but rates of hospitalizations and neutropenic fever were &amp;lt;10% in this heavily pre-treated, real-world cohort. Rates of SG dose reduction occurred in ∼50% of patients, but rates of discontinuation due to toxicity were low. GCSF prophylaxis, either primary or secondary, was used in ∼80% of patients. Additional studies are needed to clarify which patients may be at highest risk for SG-induced neutropenia and the optimal growth factor regimens to improve outcomes. Citation Format: Samantha Fisch, Joshua Chin, Laura Quintal, Melanie Majure, Michelle Melisko, Jo Chien, Hope S. Rugo, Laura A. Huppert. Single-center retrospective cohort study evaluating neutropenia and growth factor use with sacituzumab govitecan in patients with HR+/HER2- and triple negative metastatic breast cancer [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2024; 2024 Dec 10-13; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2025;31(12 Suppl):Abstract nr P5-12-25.

Prognosis of Her2-positive breast cancer has changed since the introduction of trastuzumab for treatment in metastatic and early breast cancer. It was described to be even better compared to prognosis of Her2-negative metastatic breast cancer. The purpose of this study was to evaluate the effect of trastuzumab in our cohort. Besides the effect of adjuvant pretreatment with trastuzumab on survival of patients with metastatic Her2-positive breast cancer was analyzed. All patients with primary breast cancer of the Regional Breast Cancer Center Dresden diagnosed during the years 2001-2013 were analyzed for treatment with or without trastuzumab in the adjuvant and in the metastatic treatment setting using Kaplan-Meier survival estimation and Cox regression. Age and tumor stage at time of first diagnosis of breast cancer as well as hormone receptor status, grading, time, and site of metastasis at first diagnosis of distant metastatic disease were analyzed. Of 4.481 female patients with primary breast cancer, 643 presented with metastatic disease. Her2-positive status was documented in 465 patients, including 116 patients with primary or secondary metastases. Median survival of patients with Her2-positive primary metastatic disease was 3.0years (95% CI 2.3-4.0). After adjustment for other factors, survival was better in patients with Her2-positive breast cancer with trastuzumab therapy compared to Her2-negative metastatic disease (HR 2.10; 95% CI 1.58-2.79). Analysis of influence of adjuvant therapy with and without trastuzumab by Kaplan-Meier showed a trend for better survival in not pretreated patients. Median survival was highest in hormone receptor-positive Her2-positive (triple-positive) primary metastatic breast cancer patients with 3.3years (95% CI 2.3-4.6). Prognosis of patients with Her2-positive metastatic breast cancer after trastuzumab treatment is more favorable than for Her2-negative breast cancer. The role of adjuvant chemotherapy with or without trastuzumab warrants further research. Survival is best in triple-positive metastatic breast cancer. This will effect counseling at the time of first diagnosis of metastatic breast cancer.

Palbociclib: A new breakthrough for advanced breast cancer

The phosphatidylinositol-3-kinase (PI3K) pathway is mutated and aberrantly activated in breast and other cancers and plays a key role in cancer cell proliferation and survival.1 2 The PI3K pathway is deregulated through a variety of mechanisms, including mutation or amplification of PI3K, loss or inactivation of the tumour suppressor phosphatase and tensin homolog deleted on chromosome 10 ( PTEN ), as well as activation of tyrosine kinase growth factor receptors or oncogenes upstream of PI3K.3 4 Activating mutations in PIK3CA , the gene encoding the alpha isoform (p110 α) catalytic subunit of PI3K, is present in up to 40% of patients with hormone receptor (HR)-positive, human epidermal growth factor receptor 2 (HER2)-negative breast cancers5 6 and represents a molecular target to personalise therapy of selected patients with breast cancer.2 Standard of care therapy for advanced HR-positive/HER2-negative breast cancers consists on endocrine therapy with or without the use of cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitors.7 Therapy-resistance inevitably occurs in the majority of patients. The rationale of combining PI3K inhibitors and endocrine therapy is to synergistically inhibit both the PI3K and ER pathways.8 Initial trials of pan-PI3K inhibitors plus endocrine therapy for patients with advanced breast cancer showed modest benefit with high rates of toxicity limiting their clinical drug development.9–11 Selective isoform-specific PI3K inhibitors, such as an α-specific PI3K inhibitor, have subsequently revealed activity with less toxicity.12 13 The phase III SOLAR-1 (Clinical Studies of Alpelisib in Breast Cancer 1) trial investigated the efficacy and safety of alpelisib, a α-specific class-I PI3Kinhibitor, plus fulvestrant versus placebo plus fulvestrant in patients with metastatic HR-positive/HER2-negative breast cancer who had received endocrine therapy beforehand.14 About 85.6% of patients …

Programmed death-ligand 1 (PD-L1) allows cancer cells to evade the host immune response when upregulated. PD-L1 antagonists have been shown to be effective immunotherapies. The FDA approved the PD-L1 inhibitor nivolumab for treatment of previously treated, non-responding metastatic non-small cell lung cancer (NSCLC) patients, independent of the PD-L1 status identified in tumour tissue, likely due to the controversial value of PD-L1 detection on tissue biopsy that may be out-of-date. Measurement of PD-L1 expression in circulating tumor cells (CTCs) may enable repeat testing to provide up-to-date PD-L1 status and the potential to monitor patients on these therapies. Whilst the epitope-dependent CELLSEARCH® system is the only technology FDA-cleared for the enumeration of CTCs, its application is limited to epithelial CTCs and has limited sensitivity in NSCLC. We developed a research use only assay for the characterisation of PD-L1 expression on CTCs isolated using the Parsortix® system, a label-independent microfluidic device that harvests CTCs of all phenotypes (epithelial and/or mesenchymal) based on size and compressibility. Peripheral blood (8 – 10mL) was drawn into K2EDTA tubes from 17 healthy volunteers, 17 metastatic breast cancer (MBC) patients and 18 metastatic NSCLC patients and processed on Parsortix systems within 24 hours. Harvested CTCs were cytospun and immunofluorescently stained for detection of cytokeratins and PD-L1. Slides were imaged using a BioView AllegroPlus imaging system.No CTCs were identified in the healthy volunteers, highlighting the specificity of the assay. CTCs (≥1) were identified in 70% of the MBC patients and 55% of the NSCLC patients. Importantly, the positivity rate observed in NSCLC patients was 2-fold higher than that in previously described studies using the CELLSEARCH system. A mean of 9 CTCs/tube of blood were identified in the CTC positive MBC patients, with a range of 1 – 128 CTCs. A mean of 11 CTCs/tube of blood were identified in the CTC positive NSCLC patients, with a range of 1 – 23 CTCs. CTC clusters, consisting of 3 – 45 cells per cluster, were observed in both NSCLC and MBC patients. High heterogeneity of PD-L1 expression was observed. The CTC positive patients were classified into three groups: patients with CTCs positive for both cytokeratins (CK+) and PD-L1 (36% in MBC and 40% in NSCLC), patients with a mixed population of CK+, PD-L1+/- CTCs (27% in MBC and 40% in NSCLC) and patients with CK+, PD-L1- CTCs only (36% in MBC and 20% in NSCLC).The optimized assay for detection of PD-L1 expression on CTCs allowed for the identification of PD-L1 positive and PD-L1 negative CTCs in a significant proportion of the NSCLC and MBC patients studied. The ability to isolate significant numbers of PD-L1 positive CTCs in blood lays the groundwork for development of dynamic PD-L1 monitoring to support personalized patient management. Citation Format: Mariacristina Ciccioli, Amy Davis, Ofure Alenkhe, Anne-Sophie Pailhes-Jimenez. Investigation of PD-L1 expression in circulating tumor cells isolated using the Parsortix system in metastatic lung and breast cancer patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 599.

Increased Expression of P-Glycoprotein Is Associated with Doxorubicin Chemoresistance in the Metastatic 4T1 Breast Cancer Model

Purpose: Endocrine based therapy is an effective strategy to manage hormone receptor-positive, human epidermal growth factor receptor 2-negative (HR+/HER2-) advanced breast cancer (ABC). However, nearly all patients exhibit/develop either de novo or acquired resistance. While prognostic biomarkers of endocrine responsiveness are well established for the adjuvant treatment in ER+ breast cancer, less is known regarding prognostic and predictive biomarkers of response in the first line ABC setting. We sought to develop a clinical calculator based on clinical criteria for predicting progression-free survival (PFS) and overall survival (OS) of women with HR+/HER2- ABC who will be receiving endocrine monotherapy as first-line treatment for ABC. Methods: The development of the clinical calculator will be based on data from modern clinical trials in women with HR+/HER2- ABC. The studies to be included in the final analyses are given in Table 1. The control arm data from trials1-6 will form the training dataset (N = 1,223) and be used to construct the clinical prediction models. Variables considered include age, race, ECOG status, disease measurability, body mass index, disease-free interval, number of metastatic sites, locations of metastatic sites, prior endocrine therapy, and prior chemotherapy. Missing values will be imputed using single imputation with all variables included in the imputation model. For continuous variables, restricted cubic splines will be used to determine if non-linear effects may be more appropriate. The Lasso regression will be used as a variable selection technique to reduce the dimensionality of covariates; initially all pairwise interactions will be included in the model. Following Lasso regression, the multivariable Cox proportional hazards models will be constructed for PFS and OS including only variables retained in Lasso. The final model will be internally validated for discrimination and calibration using 10-fold cross-validation. External validation will be performed using control arm data from EGF 30008 (N = 536). Results: To date, control arm data from four trials (trials 1-4) have been received. The preliminary results presented here are based on pooled data from C40503 and LEA, for which data elements have been harmonized. Models for predicting PFS and OS have good calibration and are associated with bias-corrected C-indices of 0.61 and 0.65, respectively. These models will be updated using pooled data from trials 1-6. Conclusions: Our preliminary data demonstrate that clinical calculators based on baseline clinical factors can provide accurate prediction of PFS and OS in patients with HR+/HER2- ABC treated with first-line ET. If validated, these tools may be used for risk stratification in future clinical trials and to identify patients who may require more or less aggressive therapy. Table 1:Studies to be includedTrial NumberTrial NameTrial PISample Size in Control Arm1C40503Maura Dickler152 (letrozole)2LEAMiguel Martin179 (letrozole)3FACTJonas Bergh188 (anastrozole)4FALCONJohn Robertson194 (anastrozole)5S0226Rita Mehta345 (anastrozole)6MONARCH 3Matthew Goetz165 (nonsteroidal AI)7EGF 30008Stephen Johnston536 (letrozole) Citation Format: Polley M-YC, Dickler MN, Johnston S, Goetz MP, de la Haba J, Loibl S, Mehta RS, Bergh J, Roberston J, Barlow W, Liu H, Tenner K, Martin M. A clinical calculator to predict disease outcomes in women with hormone receptor-positive advanced stage breast cancer treated with first-line endocrine therapy [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P2-07-05.