HER2 Metastatic Breast Cancer Research Articles

Genomic alterations (GA) in ESR1, PIK3CA, AKT1, and PTEN in HR(+)HER2(-) patients (pts) with metastatic breast cancer (MBC): Co-occurrence and prevalence along treatment course.

1060 Background: The standard of care for HR(+) HER2(-) MBC is evolving with new biomarker-guided drugs, including novel selective estrogen receptor degraders (SERDs) for pts with ESR1 mutations (mut) and PIK3CA and AKT inhibitors for pts with alterations in the PI3K pathway (PIK3CA, AKT1, and PTEN). This study aimed to evaluate the co-occurrence and the prevalence of these GA in different metastatic lines of therapy in real-world practice for MBC. Methods: This study included pts with HR(+) HER2(-) MBC who underwent genomic testing using Foundation Medicine tissue or liquid comprehensive genomic profiling assays, with specimens collected within 60 days of therapy initiation. Clinical data were obtained by the nationwide (US-based) de-identified Flatiron Health and Foundation Medicine real-world clinicogenomic breast cancer database (FH-FMI CGDB), originated from ~280 US cancer clinics (~800 sites of care) between 01/2011-06/2023. The prevalence of ESR1mut, PIK3CAmut, AKT1, PTENmut, and PTEN copy loss were calculated in tissue (TBx) and liquid biopsies (LBx) collected at time of 1st, 2nd, and 3rd lines of therapy. The co-occurrence of GA in TBx was evaluated. Results: Among patients with a TBx collected around therapy initiation (n=2,536), 81.5% (2,066) was collected at 1st, 10.2% (258) at 2nd, and 8.3% (212) at 3rd line. Among patients with a LBx collected around therapy initiation (n=545), 47% (256) was collected at 1st, 33.2% (181) at 2nd, and 19.8% (108) at 3rd line. In TBx, the prevalence of GA detected in 1st, 2nd, and 3rd lines were 58.6% (1,210), 67.4% (174), and 71.2% (151), respectively. In LBx, the prevalence was 42.7% (121), 65.7% (119), and 60.1% (65), respectively. Among LBx with tumor fraction ³1%, the prevalence was 67.9% (74/109), 89.1% (81/91), and 84.3% (43/51). Among patients with a GA detected in TBx 1st (n=1,210), 2nd (n=174), and 3rd (n=151) lines, both ESR1mut and a PIK3 pathway GA was detected in 7.4% (90), 12.1% (21), and 23.8% (36), respectively. Conclusions: In our dataset, 42-59% of patients with HR(+) HER2(-) MBC have at least one GA detected by TBx or LBx in 1st line, with prevalence increasing in later lines of therapy to 60-71% due to acquisition of an ESR1mut. PTEN copy loss is detected at much higher rates in TBx than LBx, consistent with the known inherent limitations of ctDNA testing. Serial genomic testing with LBx with reflex TBx if alterations are not identified should strongly be considered with the recent approvals of several molecularly targeted agents for HR(+) HER2(-) MBC. [Table: see text]

Abstract PO5-21-09: Clinical outcomes by age subgroups in the phase 3 TROPiCS-02 study of sacituzumab govitecan vs treatment of physician’s choice in HR+/HER2‒ metastatic breast cancer

Abstract Background Sacituzumab govitecan (SG) is a Trop-2directed antibody-drug conjugate approved for second-line or later (2L+) treatment of metastatic triple-negative breast cancer in multiple countries and for 2L+ treatment of HR+/HER2‒ (IHC 0, 1+, or 2+/ISH) metastatic breast cancer (mBC) in the US. SG significantly improved progression-free survival (PFS) and overall survival (OS) vs treatment of physician’s choice (TPC) in patients (pts) with pretreated, endocrine-resistant HR+/HER2‒ mBC in the TROPiCS-02 study. The incidence of HR+/HER2‒ mBC increases with age, especially after 65, and older pts often have poorer prognosis due to comorbidities, increased toxicity, and reduced efficacy of chemotherapy. In TROPiCS-02, pts aged ≥ 65 years (yr) derived consistent PFS benefit and clinically meaningful improved OS with SG vs TPC. In this analysis, we present additional efficacy and safety outcomes by age subgroup. Methods Pts with HR+/HER2‒ mBC who had received at least 1 endocrine therapy, taxane, and CDK4/6 inhibitor, and 2 to 4 prior lines of chemotherapy for mBC, were randomized to either SG (10 mg/kg IV days 1 and 8, Q3W) or TPC. The primary end point was PFS, and secondary end points included OS, objective response rate (ORR), and safety. A post hoc analysis was conducted by age subgroups (< 65 vs ≥ 65, < 75 vs ≥ 75). Results In total, 543 pts were randomized to the SG (n = 272; 73 [27%] ≥ 65, 16 [6%] ≥ 75) and TPC (n = 271; 67 [25%] ≥ 65, 8 [3%] ≥ 75) groups. Baseline characteristics were generally similar across treatment arms in each age subgroup, but a higher proportion of pts had performance status 1 vs 0 in the ≥ 65 vs < 65 and ≥ 75 vs < 75 subgroups, respectively. The data cutoff date was July 1, 2022. SG demonstrated longer median PFS and OS vs TPC across age subgroups. Hazard ratios (HR) for PFS with SG vs TPC were 0.69, 0.59, 0.70, and 0.30 for the < 65, ≥ 65, < 75, and ≥ 75 subgroups, respectively (Table). The HR for OS were 0.81, 0.80, 0.82, and 0.56 in these subgroups, respectively (Table). Median duration of response (DoR) was also longer with SG vs TPC across age subgroups, although median DoR was not estimable in the ≥ 75 subgroup (Table). ORR was higher with SG vs TPC, except in the ≥ 75 subgroup (Table). Safety was generally similar with SG vs TPC across subgroups with the following differences. Grade ≥ 3 treatment-emergent adverse events were more common in the ≥ 75 subgroup than the other subgroups (SG, 81% in ≥ 75 vs 68%-73% for all others; TPC, 71% in ≥ 75 vs 60%-61% for all others). TEAEs leading to dose reduction were also more common in pts treated with SG in the ≥ 75 subgroup, but were consistent across other subgroups (Table). However, sample sizes in the ≥ 75 subgroup were small, which limits interpretation (Table). TEAEs leading to treatment discontinuation were more common in older pts, irrespective of treatment group (Table). Conclusions SG showed benefit in PFS and OS vs TPC in pts with HR+/HER2‒ mBC across age subgroups, consistent with the intent to treat population. SG was associated with a slight increase in toxicity for elderly pts, as expected. SG demonstrated a favorable benefit/risk profile, with efficacy benefit and acceptable toxicity, for elderly pts. Table. Citation Format: Aditya Bardia, Peter Schmid, Sara Tolaney, Frederik Marmé, Javier Cortés, Theresa Valdez, Hao Wang, Wendy Verret, Hope Rugo. Clinical outcomes by age subgroups in the phase 3 TROPiCS-02 study of sacituzumab govitecan vs treatment of physician’s choice in HR+/HER2‒ metastatic 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 PO5-21-09.

Abstract PO1-17-05: Real-world effectiveness of palbociclib plus aromatase inhibitors (AI) in metastatic breast cancer patients with cardiovascular diseases

Abstract Background Breast cancer survivors are at risk for mortality from cardiovascular diseases (CVD). CVD and their treatments can impact breast cancer treatment selection and clinical outcomes. A cyclin dependent kinase 4/6 inhibitor (CDK4/6i) combined with endocrine therapy (ET) is more effective than ET alone for hormone receptor-positive/human epidermal growth factor receptor 2-negative (HR+/HER2) metastatic breast cancer (MBC). CDK4/6i plus ET is now the standard of care in the first-line setting for HR+/HER2 MBC. However, data on the effectiveness of CDK4/6i in MBC patients with CVD are limited. We compared overall survival (OS) and real-world progression-free survival (rwPFS) of palbociclib plus AI (PAL+AI) vs AI alone in HR+/HER2 MBC patients with CVD in routine US clinical practices. Methods The Flatiron Health longitudinal database contains electronic health records from >280 cancer clinics, representing >3 million actively treated cancer patients in the US. Using the Flatiron database, we conducted a retrospective analysis of 469 patients with HR+/HER2 MBC and CVD who started PAL+AI or AI as first-line therapy between February 2015 and March 2020. CVD prior to the initiation of PAL+AI or AI were identified based on their definitions within the National Cancer Institute-Comorbidity Index (NCI-CI), including myocardial infarction, congestive heart failure, peripheral vascular diseases, and cerebrovascular diseases. Patients were assessed from start of PAL+AI or AI to September 30, 2020 (data cutoff date), death, or last visit, whichever came first. OS was defined as months from start of PAL+AI or AI to death. rwPFS was defined as months from start of PAL+AI or AI to death or disease progression, evaluated based on clinical assessment or radiographic scan/tissue biopsy. Stabilized inverse probability treatment weighting (sIPTW) as primary analysis was used to balance baseline demographics and clinical characteristics. Cox proportional-hazards models were used to estimate the relative effectiveness of PAL+AI vs AI alone. Results Of the 469 eligible patients, 160 (34.1%) were treated with PAL+AI and 309 (65.9%) were treated with AI alone. Compared with AI-alone patients, those treated with PAL+AI were younger and were more likely to have de novo MBC, ≥2 metastatic sites, and lung/liver involvement. After sIPTW, patient characteristics were generally balanced. After sIPTW, median OS (95% confidence interval [CI]) was 40.7 months (30.956.0) in PAL+AI patients and 26.5 months (23.337.3) in AI patients (hazard ratio [HR]=0.732, 95% CI=0.5370.997, p=0.0476). Median rwPFS (95% CI) was 20.0 months (11.7–27.5) in PAL+AI patients and 12.5 months (9.718.3) in AI patients (HR=0.679, 95% CI=0.5120.900, p=0.0070). Consistent results were observed with multivariate Cox proportional-hazards models as sensitivity analysis. See Table for baseline patient characteristics and outcome results. Conclusions First-line PAL in combination with AI is associated with prolonged OS and rwPFS in patients with HR+/HER2 MBC and CVD in a real-world setting compared with AI alone. Further studies with larger cohorts and comprehensive assessments of comorbidities are needed to provide additional evidence of outcomes and safety of CDK4/6i plus AI for MBC patients with various comorbid conditions in routine clinical practice. Citation Format: Adam Brufsky, Xianchen Liu, Benjamin Li, Lynn McRoy, Connie Chen, Doris Makari, Rachel Layman, Hope Rugo. Real-world effectiveness of palbociclib plus aromatase inhibitors (AI) in metastatic breast cancer patients with cardiovascular diseases [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 PO1-17-05.

Abstract PO2-16-05: ESR1 mutations (ESR1mut) in HR(+)HER2(-)patients with metastatic breast cancer (MBC): prevalence along treatment course and predictive value for endocrine therapy (ET) resistance in real-world practice

Abstract Background: ET combined with CDK4/6 inhibitors (CDKi) is the standard of care for HR(+)HER2(-) patients with MBC. ESR1mut is an acquired resistance mechanism to ET, especially aromatase inhibitors (AI). The prevalence and behavior of ESR1mut in patients receiving the selective estrogen receptor degrader (SERD) fulvestrant remains in question. This study aimed to characterize the prevalence of ESR1mut at start of successive lines of therapy and to evaluate clinical outcomes of ET by ESR1 status in 1st line therapy in real-world practice. Methods: This study included patients with HR(+)HER2(-) MBC who underwent genomic testing using Foundation Medicine tissue or liquid comprehensive genomic profiling (CGP) assays, with specimens collected within 60 days of therapy initiation. Patient clinical data was obtained by the nationwide (US-based) de-identified Flatiron Health and Foundation Medicine real-world clinicogenomic breast database (FH-FMI CGDB), originated from ~280 US cancer clinics (~800 sites of care) between 01/2011 and 04/2023. ESR1mut prevalence was calculated in tissue and liquid samples collected in the 1st, 2nd, and 3rd lines of therapy. Real-world progression free-survival (rwPFS), time to treatment discontinuation (rwTTD), and overall survival (rwOS) were compared between patients who received AI + CDKi and between patients receiving fulvestrant + CDKi 1st line therapy [ESR1mut vs. ESR1 wild-type (wt) by tissue CGP] by Cox models. Multivariable analyses adjusted for adjuvant therapy, age, ECOG, menopausal status, histology, stage at diagnosis, metastatic site, and specific ESR1mut (Y537S, D538G, E380W, or others) were performed. Results: The prevalence of ESR1mut in tissue samples collected in 1st, 2nd, and 3rd lines of therapy was 7.9% (n=159/2004), 26.4% (n=66/250), and 34.0% (n=68/200), respectively. The prevalence of ESR1mut in liquid samples collected in the 1st, 2nd, and 3rd lines of therapy was 11.6% (n=30/259) 34.4% (n=63/183), and 35.9% (n=42/117), respectively. Among patients receiving AI + CDKi 1st line therapy (n=485), those with ESR1mut vs. ESR1wt had less favorable rwPFS [median 6.1 vs. 20.8 months, hazard ratio (HR) 2.36, 95% CI 1.35-4.14, p=0.003]. rwTTD and rwOS assessments were consistent with the magnitude of effect of rwPFS. Among patients receiving fulvestrant + CDKi 1st line therapy (n=302), those with ESR1mut vs. ESR1wt had less favorable rwPFS (median 10.5 vs. 14.5 months, HR 1.5, 95% CI 1.05-2.15, p=0.025), but no difference was observed for rwTTD and rwOS (p >0.05). Notably, the multivariable analyses found the independent association of ESR1mut and less favorable rwPFS (HR 2.18, 95% CI 1.15-4.1, p=0.018), rwTTD (HR 3.34, 95% CI, 1.84-6.1, p< 0.001), and rwOS (HR 2.46, 95% CI 1.04-5.9, p=0.041) in patients receiving AI + CDKi. The multivariable analyses confirmed no association between ESR1mut and outcomes in patients receiving fulvestrant + CDKi (p >0.05). No substantial differential associations were observed between specific ESR1mut and clinical outcomes in the multivariable analyses. Conclusion: In our dataset, ESR1mut is prevalent in about 8-11% of baseline tissue and liquid samples of patients with HR(+)HER2(-) MBC. Baseline ESR1mut is associated with less favorable outcomes in patients receiving AI + CDKi 1st line therapy, but not in patients receiving fulvestrant + CDKi. Specific ESR1mut do not seem to be associated with different outcomes to ET. ESR1mut prevalence increased during treatment course. Further investigation is warranted to determine optimal endocrine partner with CDKi based upon ESR1 status, particularly with development of oral SERDs. Citation Format: Manali Bhave, Julia Quintanilha, Ryon Graf, Takara Scott, Hanna Tukachinsky, Gerald Li, Alexa Schrock, Geoffrey Oxnard, Mia Levy, Kevin Kalinsky. ESR1 mutations (ESR1mut) in HR(+)HER2(-)patients with metastatic breast cancer (MBC): prevalence along treatment course and predictive value for endocrine therapy (ET) resistance in real-world practice [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 PO2-16-05.

Abstract PO1-04-06: Exposure-response analyses of sacituzumab govitecan efficacy and safety in patients with metastatic breast cancer

Abstract Background: Sacituzumab govitecan (SG) is an antibody-drug conjugate that is composed of an anti Trop-2 antibody coupled to the cytotoxic SN-38 payload via a proprietary, hydrolysable CL2A linker. SG (10 mg/kg on D1 and D8 of every 21D cycle) is approved for patients (pts) with metastatic triple-negative breast cancer (mTNBC) who received ≥2 prior systemic therapies (≥1 in the metastatic setting). The relationship between exposure of SG, free SN-38, and total antibody (tAB) following SG administration and its efficacy and safety were evaluated in pts with HR+/HER2‒ metastatic breast cancer (mBC) and all pts with mBC (mTNBC or HR+/HER2‒ mBC), respectively. Methods: Available exposure and efficacy outcomes from HR+/HER2‒ mBC pts from phase 3 study TROPiCS-02 (n=260) and safety outcomes from mBC pts in phase 1/2 study IMMU-132-01, phase 3 study ASCENT and TROPiCS-02 (total n=569) were analyzed. Exposure-response (ER) models were developed to characterize the relationship between exposure and efficacy (complete response [CR], overall response rate [ORR], clinical benefit rate [CBR], overall survival [OS] and progression-free survival [PFS]) and safety (adverse events [AEs] of vomiting, diarrhea, hypersensitivity reactions, nausea, neutropenia, febrile neutropenia, time to first dose reduction and first dose delay) endpoints. Exposure metrics of SG, free SN-38, and tAB were evaluated as predictors and effect of clinically relevant covariates was characterized within the modeling framework. Results: Average SG-related serum exposures over the duration of treatment (until the event) were associated with significantly increased efficacy (probability of CR, ORR, CBR and longer OS and PFS) and safety events (probability of any grade AE). Neutropenia was the only AE where the increase in exposure was significantly associated with the increased probability of Grade ≥3 and Grade 4 events. Baseline Trop-2 expression level was not correlated with assessed efficacy and safety endpoints. Conclusions: Within the exposure range achieved with the 10 mg/kg regimen, higher exposure values were associated with a higher probability of achieving better efficacy. The 10 mg/kg SG dose achieved an acceptable balance between efficacy and safety which supports the appropriateness of this regimen in pts with HR+/HER2‒ mBC. Citation Format: Indrajeet Singh, Abhishek Sathe, Paul Diderichsen, Han Witjes, Arne Van Schanke, John Maringwa, Wendy Verret, Sandhya Girish, Ahmed Othman. Exposure-response analyses of sacituzumab govitecan efficacy and safety in patients with metastatic 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 PO1-04-06.

HTA84 Cost-Utility Analysis of Talazoparib Versus Chemotherapy for Patients with Breast Cancer HER2- with Mutation in the BRCA1/2 Gene from the Brazilian Private Healthcare System

Breast cancer is the most common form of neoplasm in women in Brazil, being the main cause of death from cancer in this population. The aim of this analysis is to compare effectiveness and incremental costs between talazoparib and standard chemotherapy the treatment of metastatic breast cancer HER2- with mutation in the BRCA1/2 gene, from the perspective of the Brazilian private healthcare system.

Randomised open-label phase II study of induction standard of care fulvestrant and CDK4/6 inhibition with addition of ipatasertib in metastatic ER+/HER2- breast cancer patients without circulating tumour (ct) DNA suppression (FAIM).

TPS1111 Background: The combination of fulvestrant and one of the three approved CDK4/6 inhibitors (i) is the standard of care for patients with ER+/HER2 metastatic breast cancer progressing on first-line endocrine therapy, or relapsing on or within a year of completing adjuvant endocrine therapy. AKT inhibition combined with fulvestrant has recently demonstrated clinically important activity in patients with advanced ER+/HER2- breast cancer progressing on first-line CDK4/6i plus an AI. Monitoring ctDNA dynamics has potential utility as an early response evaluation tool: Lack of suppression of ctDNA at day 15 in patients treated with palbociclib and fulvestrant in the PALOMA-3 trial was predictive for shorter PFS. We designed FAIM to establish whether the addition of the AKT inhibitor, ipatasertib, improves PFS in patients with poor ctDNA suppression during cycle 1 of fulvestrant and CDK4/6i. Methods: FAIM is a phase 2 multi-centre, randomised, open-label superiority trial in patients with ER+/HER2- advanced breast cancer, recruiting at centres in the UK. Patients will undergo ctDNA testing at days 1 and 15 of cycle 1 fulvestrant and CDK4/6 inhibitor. Eligible patients must be aged ≥18, have ER+ (≥1% or Allred score 3/8 or greater) and HER2- advanced breast cancer, measurable disease or assessable bone disease (RECIST 1.1), adequate organ function, fasting glucose ≤150mg/dL and HbA1c ≤7.5% and be eligible for NHS treatment with fulvestrant and CDK4/6i. Patients with diabetes requiring insulin, significant cardiac disease, a history of pneumonitis, or prior exposure to CDK4/6i are excluded. The FoundationOne Liquid CDx assay will be used for ctDNA analysis, a pan-cancer, tumour-agnostic liquid biopsy test that uses error-corrected next-generation sequencing. Patients with poor ctDNA suppression at day 15 will be eligible for the randomised (minimisation) study. Up to 483 patients starting fulvestrant andCDK4/6i will enroll for ctDNA screening to allow 174 patients to enter the randomised study. The primary endpoint of the study is to compare PFS in patients randomised to palbociclib/fulvestrant +/- ipatasertib. Secondary endpoints include safety, overall survival and overall response rate in all randomised patients and PFS in the sub-group of patients with alterations in the PIK3CA/AKT1/PTEN pathway. One hundred patients with ctDNA suppression at day 15, and up to 50 patients with no detectable ctDNA at day 1, will form additional control groups for exploratory outcome comparison to patients with poor ctDNA suppression. Enrolment began in December 2022 and is anticipated to continue for 2 years (NCT04920708). Clinical trial information: NCT04920708 .

Post-CDK 4/6 Inhibitor Therapy: Current Agents and Novel Targets

Front-line therapy for advanced and metastatic hormone receptor positive (HR+), HER2 negative (HER-) advanced or metastatic breast cancer (mBC) is endocrine therapy with a CDK4/6 inhibitor (CDK4/6i). The introduction of CDK4/6i has dramatically improved progression-free survival and, in some cases, overall survival. The optimal sequencing of post-front-line therapy must be personalized to patients' overall health and tumor biology. This paper reviews approved next lines of therapy for mBC and available data on efficacy post-progression on CDK4/6i. Given the success of endocrine front-line therapy, there has been an expansion in therapies under clinical investigation targeting the estrogen receptor in novel ways. There are also clinical trials ongoing attempting to overcome CDK4/6i resistance. This paper will review these drugs under investigation, review efficacy data when possible, and provide descriptions of the adverse events reported.

Effect of Surface Decalcification With Hydrochloric Acid on the Determination of Estrogen Receptor, Progesterone Receptor, Ki67, and Human Epidermal Growth Factor Receptor 2 Expressions in Invasive Breast Carcinoma Based on Immunohistochemistry and Fluorescence In Situ Hybridization.

Bone is the most common site of metastatic breast cancer (MBC). EDTA is often used to decalcify bony tissue samples to ensure the accurate assessment of antigenicity in MBC. It takes ~24 to 48 hours to decalcify small bone tissues such as bone marrow, which is considered unacceptable given the priority that is often placed on the rapid processing of bone marrow trephine cores. Thus, an effective decalcification method that preserves genetic material is needed. We performed immunohistochemical studies on surface decalcification (SD) in breast tumors and evaluated the effect of SD on receptor status and human epidermal growth factor receptor 2 (HER2). Fluorescence in situ hybridization was performed on a subset of these tumors to establish a protocol for handling bone specimens for MBC. Forty-four cases of invasive breast tumors were studied. We compared the immunohistochemical expressions of estrogen receptor (ER), progesterone receptor (PR), Ki67, and HER2 between control tissue (nondecalcified) and parallel tissue subjected to SD with hydrochloric acid. We also evaluated the effect of SD on the fluorescence in situ hybridization expression of HER2. Categorical decreases in ER and PR expression were identified in 9/31 (29.0%) cases without SD and 10/26 (38.5%) cases with SD. HER2 expression changed from equivocal to negative in 4/12 (33.4%) cases. Among the HER2-positive cases, all remained positive after SD. The most significant declines in immunoreactivity occurred with Ki67, with an average decrease from 22% to 13%. The average HER2 copy numbers were 5.37 and 4.76 in the control and SD groups, respectively, and the average HER2/CEP17 ratios were 2.35 and 2.08, respectively. Overall, SD is an alternative decalcification method in bony metastases to assess ER, PR, and HER2 in MBC.

Mechanisms of Resistance to CDK4/6 Inhibitors and Predictive Biomarkers of Response in HR+/HER2-Metastatic Breast Cancer—A Review of the Literature

The latest and newest discoveries for advanced and metastatic hormone receptor-positive (HR+) and human epidermal growth factor receptor 2-negative (HER2-) breast cancer are the three cyclin-dependent kinases 4 and 6 inhibitors (CDK4/6i) in association with endocrine therapy (ET). However, even if this treatment revolutionized the world and continued to be the first-line treatment choice for these patients, it also has its limitations, caused by de novo or acquired drug resistance which leads to inevitable progression after some time. Thus, an understanding of the overview of the targeted therapy which represents the gold therapy for this subtype of cancer is essential. The full potential of CDK4/6i is yet to be known, with many trials ongoing to expand their utility to other breast cancer subtypes, such as early breast cancer, and even to other cancers. Our research establishes the important idea that resistance to combined therapy (CDK4/6i + ET) can be due to resistance to endocrine therapy, to treatment with CDK4/6i, or to both. Individuals' responses to treatment are based mostly on genetic features and molecular markers, as well as the tumor's hallmarks; therefore, a future perspective is represented by personalized treatment based on the development of new biomarkers, and strategies to overcome drug resistance to combinations of ET and CDK4/6 inhibitors. The aim of our study was to centralize the mechanisms of resistance, and we believe that our work will have utility for everyone in the medical field who wants to deepen their knowledge about ET + CDK4/6 inhibitors resistance.

A retrospective, non-interventional study of breast cancer patients diagnosed with ER+/HER2 negative, locally advanced or metastatic breast cancer treated with palbociclib in Denmark

BackgroundThe recommended first-line treatment for advanced, ER+/HER2 negative breast cancer is a CDK 4/6 inhibitor in combination with an endocrine backbone. This study investigated the use of palbociclib, as first- or second-line therapy for advanced breast cancer patients in a real-world setting.Material and MethodsThis retrospective, population-based study included all Danish, advanced breast cancer patients with ER+/HER2 negative disease who initiated first- or second-line treatment with palbociclib from January 1st, 2017, until December 31st, 2020. The primary outcomes were PFS and OS.ResultsThe study included 1054 advanced breast cancer patients with a mean age of 66.8 years. Median OS was 51.7 months (95% CI, 44.9–54.6) for all patients in the first-line setting (n = 728) and median PFS was 24.3 months (95% CI, 21.7–27.8). Patients treated in second line (n = 326) had a median OS of 32.5 months (95% CI, 29.9–35.9) and a median PFS of 13.6 months (95% CI, 11.5–15.7). In first-line setting, the PFS and OS were significantly different for endocrine sensitive patients treated with AI (aromatase inhibitor) (n = 423) vs. fulvestrant (n = 158) as endocrine backbone to palbociclib (median PFS AI 31.3 months vs fulvestrant 19.9 months, p = 0.002 and median OS AI 56.9 months vs. fulvestrant 43.6 months, p = 0.001). In endocrine resistant patients (n = 145), no statistically significant difference in PFS was shown (median PFS AI 21.5 months vs. fulvestrant 12.0 months, p = 0.09), whereas OS was significantly different (median OS AI 43.5 months vs. fulvestrant 28.8 months, p = 0.02).ConclusionIn this real-world study, treatment with palbociclib combination therapy met the standards of efficacy set by the phase III trials, PALOMA-2 and PALOMA-3, and the standards set by real-world studies in other countries. The study showed significantly different outcomes in terms of PFS and OS in endocrine sensitive patients comparing AI vs. fulvestrant as endocrine backbone to palbociclib as first-line therapy.

Abstract P4-01-20: Phase IV study evaluating talazoparib in patients with locally advanced or metastatic negative HER2 breast cancer and a somatic or germline BRCA1/2 mutation (ViTAL) – Analysis of cohort 1 according to hormonal receptor status

Abstract Background: Talazoparib (TALA) is a highly potent, dual-mechanism PARP inhibitor that has demonstrated clinical benefit in EMBRACA Phase III trial for patients with germline BRCA1/2 mutated locally advanced or metastatic HER2- breast cancer. Objective: The aim of the study is to ensure the effectiveness and safety of TALA in real-life setting among patients with locally advanced or metastatic HER2- breast cancer, with somatic or germline BRCA1/2 mutation. Methods: ViTAL is an ambispective, multicentric, longitudinal, phase IV study. It includes two ambispective cohorts: - Cohort 1: patients treated through the French Early Access Program and inclusion of patients with somatic BRCA1/2 mutation was allowed. - Cohort 2: patients treated according to the European Marketing Approval granted in 09/21/2021. Here we present the results of the primary and some secondary endpoints for cohort 1. Results: From November 2018 to May 2021, 86 patients were included in Cohort 1, with updated results after a median follow-up of 17.3 months (11.2 - 24.4). Patients’ characteristics are 53.5% of ER+ BC/46.5% of TNBC (refer to the table). The median Time to Treatment Discontinuation (mTTD) was 9.0 months [range 6.0; 11.5] with 37.7% of patients still on treatment at 12 months. Subgroup analysis shows similar mTTD according HR status, germline vs somatic mutation and prior platinum exposure (refer to the table). The Clinical Benefit Rate assessed by the investigators is 82.4% (Complete Response for 25.7%, Partial response R for 32.4% and stable disease for 24.3%). The median of duration of CNS metastases control was 6.6 months, and 80.0% of patients had control of CNS metastases during TALA. Out of the 85 treated patients, 69 patients (80,2%) experienced a TALA permanent discontinuation for progressive disease (84.1%), toxicity (10.1%), cancer-related death (1.4%), or other reasons (1.4%). After discontinuation of TALA, 65.1% of patients received a subsequent treatment with a TTD of 2.3 months [1.7; 2.7]. The most common subsequent treatments were non-platinum chemotherapy (64.3%), platinum chemotherapy (19.6%) and others (19.1%). At least one adverse events (AEs) was recorded in 74.4% of patients. Hematologic AEs (any grade) occurred in 48.8% (anemia 27.9%, thrombocytopenia 12.8%, neutropenia 10.5%). Most common non-hematologic AEs were alopecia (8.1%) and asthenia (7.0%). Related Serious Hematologic AEs occurred in 10 patients (11.6%) including 7 (8.1%) Anemia. Related Serious Non-hematologic AEs (vomiting, pyelonephritis and ascitis) were seen in 3 patients (3.6%). AEs associated with temporary drug interruption, dose modification and permanent drug discontinuation occurred in 36 (41.9%), 24 (27.9%), and 7 (10.1%) patients respectively. The mOS is expected to be reached at the time of the congress, with 51.9% of patients still alive at 24 months. Conclusions: ViTAL is the largest study that reports real-word data with TALA. Outcomes and safety in Cohort 1 are consistent with the results of EMBRACA study and give additional data on subgroups of interest (ie patients previously treated with carboplatin, presence of CNS). (Litton et al. NEJM 2018) mTTD on subgroups of interest Patients’ characteristics Citation Format: Delphine Loirat, Marie Duboys de la barre, Jean-Christophe Thery, Ioana Hrab, Christelle Jouannaud, Jean-Loup Mouysset, Laura Salabert, Pauline Soibinet, Audrey Mailliez, Romain Valery, Anne Creisson, Cristian Villanueva, Nadine Dohollou, Jean-david Fumet, Thomas grellety, Nathalie Perez-staub, Emma Lachaier, Aurore Iltis-roux, Miguel delbado, Abeer Najem, Romuald Le Scodan, Elsa Curtit, kais aldabbagh, Pascal Pujol, thibault DE LA MOTTE ROUGE. Phase IV study evaluating talazoparib in patients with locally advanced or metastatic negative HER2 breast cancer and a somatic or germline BRCA1/2 mutation (ViTAL) – Analysis of cohort 1 according to hormonal receptor status [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P4-01-20.

Abstract P4-01-04: Phase IV multicenter study evaluating RWE and the safety of talazoparib in patients with locally advanced or metastatic negative HER2 breast cancer and a BRCA1/2 mutation (ViTAL) - Cohort 2: patients treated according to the EMA

Abstract Background: Talazoparib (TALA) is a highly potent, dual-mechanism PARP inhibitor that has demonstrated clinical benefit in EMBRACA Phase III trial for patients with germline BRCA1/2 (BRCA1/2)-mutated locally advanced or metastatic HER2- breast cancer. Objective: The aim of the study is to ensure the effectiveness and safety of TALA in the real-world setting among patients with locally advanced or metastatic HER2- breast cancer, with somatic or germline BRCA1/2 mutation. Methods: ViTAL is an ambispective, multicentric, longitudinal, phase IV study. It includes two ambispective cohorts: - Cohort 1: patients treated through the French Early Access Program and inclusion of patients with somatic BRCA1/2 mutation was allowed. - Cohort 2: patients treated according to the European Marketing Approval granted in 09/21/2021. The primary endpoint of the study is the Time to Treatment Discontinuation (TTD) which is defined as time between the date of first dose of TALA and the date of last dose or death. Results: From November 2018 to May 2021, 85 patients were included in Cohort 2, Patients’ characteristics are: - a median age of 49.0 years; - 65.8% ER+ BC/34.2% TNBC; - 42.1% mBRCA1/55.3 % mBRCA2/2,6% mBRCA1 and mBRCA2. - 85.7% ECOG PS 0 or 1; - 23.4% de novo mBC. - Visceral, bones and CNS metastases were found in 59.0%, 61.5% and 10.3% of patients respectively. - No breast or ovarian cancer family history at 1st degree was found in 39 patients (50.0%). - 38.5% were chemo-naïve; - 21.8% received prior platinum in (neo)adjuvant or metastatic setting, with a median of prior cytotoxic regimen of 1 - For patients with ER+/HER2- ABC the median number of prior endocrine therapy was 1 and 62.0% of these patients received a CDK4/6 inhibitor prior to TALA. - 8 patients (10.3%) had CNS metastases. Out of the 78 treated patients, 57 patients (73.0%) experienced a TALA permanent discontinuation for Progressive disease (80.7%), toxicity (12.3%), cancer-related death (1.8%), or other reasons (1.8%). The median TTD for TALA is 9.6 months [6.7;10.8] with 34.5% of patients still on treatment at 12 months. After discontinuation of TALA, 59.0% of patients received a subsequent treatment with a TTD of 3.9 months [2.1; 45]. The most common subsequent treatments were non-platinum chemotherapy (67.4%), platinum therapy (6.5%) and other (26.1%). The Clinical Benefit Rate assessed by the investigators is 87.6% (Complete Response for 14.1%, Partial Response for 56.3% and Stable Disease for 17.2%). The median duration of CNS metastases control was 10.2 months, and 25.0% of patients had a control of CNS metastases. At least one adverse events (AEs) was recorded in 67.9% of patients. Hematologic adverse events (AEs) (any grade) occurred in 55.1% (anemia 37.2%, thrombocytopenia 16.7%, neutropenia 15.4%). Most common non-hematologic AEs were Nausea (15.4%) and asthenia (15.4%). Related Serious Hematologic AEs occurred in 6 patients (7.7%) including 3 (3.8%) thrombocytopenia and 3 (3.8%) anemia. Related Serious Non-hematologic AEs (metrorrhagia) were seen in 1 patient (1.3%). AEs associated with temporary drug interruption, dose modification and permanent drug discontinuation occurred in 26 (33.3%), 22 (28.2%), and 7 (12.3%) patients respectively. The mOS is not mature for this analysis. Conclusions: ViTAL is the largest study that reports real-word data with TALA. Outcomes and safety in Cohort 2 (patients treated with TALA according to the European Marketing Approval), are consistent with the results of EMBRACA study and with the Cohort 1. (Litton et al. NEJM 2018) Citation Format: Delphine Loirat, Marie Duboys de la barre, Cristian Villanueva, Audrey Mailliez, Nicolas Isambert, Lionel Moreau, Emmanuelle Jacquet, Dominique Spaëth, Anne Creisson, Christelle Jouannaud, Eric Legouffe, Miguel delbado, Laura Deiana, Pauline Soibinet, Ioana Hrab, Thomas grellety, Nadine Dohollou, Raffaele Longo, Jean-Christophe Thery, Jean-david Fumet, Sellam Zineb, Pascal Pujol, thibault DE LA MOTTE ROUGE. Phase IV multicenter study evaluating RWE and the safety of talazoparib in patients with locally advanced or metastatic negative HER2 breast cancer and a BRCA1/2 mutation (ViTAL) - Cohort 2: patients treated according to the EMA [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P4-01-04.

Real-world treatment outcomes in HR+ HER2- metastatic breast cancer patients treated with CDK4/6 inhibitors: Results from a reference center in Brazil

BackgroundCyclin-dependent kinase 4/6 inhibitors (CDK4/6i) have been recently developed and introduced into clinical practice. MethodsWe retrospectively analyzed data from patients with confirmed HR+/HER2 metastatic breast cancer treated with hormonal therapy in combination with ribociclib (R), palbociclib (P), or abemaciclib (A). Outcomes: median progression-free survival (mPFS), time to treatment discontinuation (mTTD), and objective response rate (ORR). ResultsBetween January 2016 - June 2021, 142 patients were treated with an CDK4/6i (79 P, 42 R, 21 A). The median age was 59 years and 67.6% had recurrent disease. Roughly 35.2%, 36.6%, 28.2% of the patients had 1, 2 or 3+ metastatic sites, respectively, and 55.6% of the patients received CDK4/6i as a first-line treatment. The mPFS was 28m(R) vs. 14m(P) vs. 6m(A) (P = 0.002), with a higher proportion of patients receiving R in the first-line setting. However, no difference was seen when the analysis was restricted to the first-line scenario (P = 0.193). Sixty-four patients required one dose reduction, and 19 patients required two. ORR was 76.2% (R) vs 62% (P) vs 42.9% (A). More patients achieved a complete response with R and P, with no difference in the incidence of partial response and stable disease. Adverse events occurred in 94.4% of the population, with the most common grade 3–4 AE being neutropenia (59.1%). ConclusionsOur results confirm the efficacy and tolerability of CDK4/6i in routine clinical practice. This is the first real-world data describing and comparing the efficacy and toxicity of CDK4/6i in the Brazilian population.

Search for predictors of the efficiency of treatment with CDK4/6 inhibitors with HR+/HER2 metastatic breast cancer

Search for predictors of the efficiency of treatment with CDK4/6 inhibitors with HR+/HER2 metastatic breast cancer

Antibody-drug conjugates targeting TROP-2: Clinical development in metastatic breast cancer

Antibody drug conjugates (ADCs) combine the potent cytotoxicity of chemotherapy with the antigen -specific targeted approach of antibodies into one single molecule. Trophoblast cell surface antigen 2 (TROP-2) is a transmembrane glycoprotein involved in calcium signal transduction and is expressed in multiple tumor types. TROP-2 expression is higher in HER2-negative breast tumors (HR+/HR-) and is associated with worse survival. Sacituzumab govitecan (SG) is a first-in-class TROP-2-directed ADC with an anti-TROP-2 antibody conjugated to SN-38, a topoisomerase inhibitor via a hydrolysable linker. This hydrolysable linker permits intracellular and extracellular release of the membrane permeable payload enabling the “bystander effect” contributing to the efficacy of this agent. There was significant improvement in progression free survival (PFS) and overall survival (OS) with SG versus chemotherapy in pretreated metastatic triple negative breast cancer (TNBC), resulting in regulatory approval. Common adverse events (AE) reported were neutropenia and diarrhea. SG also demonstrated clinical activity versus chemotherapy in a phase III trial of HR+/HER2-metastatic breast cancer (MBC) and is under evaluation in first-line metastatic and early stage TNBC as well. Datopotamab deruxtecan (Dato-DXd) is a TROP-2 ADC that differs from SG in that it has a cleavable tetrapeptide linker and a more potent topoisomerase inhibitor payload. This construct is highly stable in circulation with a longer half-life than SG, and undergoes cleavage in presence of intracellular lysosomal proteases. Dato-DXd demonstrated preliminary efficacy in unselected metastatic TNBC, with common AEs of low-grade nausea and stomatitis. Dato-DXd is being investigated in phase III studies in metastatic TNBC and HR+/HER2- MBC. These novel TROP-2 ADCs have the potential to deliver enhanced efficacy with reduced toxicity in MBC and possibly in early stage breast cancer (EBC).

Clinical outcomes of cyclin-dependent kinase 4–6 (CDK 4–6) inhibitors in patients with male breast cancer: A multicenter study

BackgroundSince breast cancer is less common in men than in women, data on the use of new therapeutic agents, including cyclin-dependent kinase 4–6 (CDK 4–6) inhibitors, are limited in patients with metastatic hormone receptor positive (HR+), human epidermal growth factor receptor 2-negative (HER2-) male breast cancer. Therefore; we aimed to investigate the treatment responses of metastatic HR+, HER2-male breast cancer patients treated with CDK 4–6 inhibitors in a multicenter real-life cohort. MethodsMale patients with a diagnosis of HR+ and HER2-metastatic breast cancer, treated with any CDK 4–6 inhibitor, were included in the study. Demographic and clinical characteristics of the patients were recorded. We aimed to determine progression-free survival (PFS) time, response rates and drug related side effects. ResultsA total 25 patients from 14 institutions were recruited. The mean age at diagnosis was 57 years. Median follow-up was 19.53 (95% CI: 14.04–25.02) months. The overall response rate was 60%. While the median PFS was 20.6 months in the whole cohort, it wasn't reached in those using CDK 4–6 inhibitors in first line and 10 months in the subsequent lines (p:0.009). No new adverse events were encountered. ConclusionIn our study, we found that CDK 4–6 inhibitors are effective and safe options in men with HR+ and HER2-metastatic breast cancer as in women. Our results support the use of CDK 4–6 inhibitor-based combinations in the first-line treatment of HR+ and HER2-metastatic male breast cancer.

Single center experience with alpelisib-fulvestrant in heavily pretreated women with HR(+), HER-2 (−) metastatic breast cancer.

e13034 Background: HR-positive, Her2-negative metastatic breast cancer patients harboring PIK3CA mutations are associated with resistance to endocrine therapy and worse prognosis. Results from the phase III SOLAR-1 trial demonstrate improved PFS for patients treated with Alpelisib-Fulvestrant after failure on first or second line treatment with aromatase inhibitor. Methods: Within an early access program for Alpelisib in a single oncology center, patients diagnosed with metastatic HR-positive, Her2 -negative breast cancer were screened for PIK3CA mutations. New generation sequencing (NGS) was the preferred technique to identify carriers with PIK3CA mutations on soft tissue or liquid biopsy. Patients who progressed and carried PIK3CA mutations received Alpelisib and fulvestrant as subsequent line of therapy. Results: Among 32 patients (pts) screened, 13 (40,6%) had a PIK3CA mutation. In total, 11 pts received alpelisib. Median age at diagnosis was 57.5 years (range, 39-69). Eight pts (72.7%) had been operated for early-stage breast cancer, 6 (54.5%) had received adjuvant chemotherapy and 5 (45.5%) had received adjuvant radiotherapy. Of 11 pts with evaluable histology, 3 pts (27.3%) had high grade tumors at diagnosis. Ten pts (90.9%) had PR positive tumors. Median Ki67 was 20% (range, 2-80). Eight pts (72.7%) had PIK3CA exon 20 and 3 (27.3%) had exon 9 mutations. Six pts (54.5%) had received prior chemotherapy in the metastatic setting and 10 (90.9%) prior CDK4/6 inhibitor. Three pts (27.3%) received Alpelisib as 2nd line and all remaining patients received alpelisib beyond 3rd line treatment. All pts (100%) had metastasis to the bones, 8 pts (72.7%) to the liver, 6 pts (54.5%) to the lungs and 2 pts (18.2%) to the brain. Until the date of last assessment, Alpelisib was administered for a median of 5.1 months (range, 0.4-21.3). Ten pts were evaluable for response to treatment with Alpelisib. One (10%) had CR, 5 (50%) SD and 4 (40%) PD as best response. Median duration of disease control was not reached. Baseline characteristics were not associated with disease control. Adverse events noticed were thrombocytopenia grade II (1/11), diarrhea grade II (2/11), skin rash grade I &II (4/11), weakness grade III (1/11) and hyperglycemia (3/11). Conclusions: Prevalence of PIK3CA mutations is consistent with published data. Furthermore, combination of Alpelisib-Fulvestrant is a highly active line of therapy even in heavily pretreated patients.

Abstract PD13-01: Balixafortide (a CXCR4 antagonist)+eribulin versus eribulin alone in patients with HER2 negative, locally recurrent or metastatic breast cancer: An international, randomized, phase 3 trial (FORTRESS)

Abstract Background: Balixafortide (B), a synthetic cyclic peptide, is a potent selective CXCR4 antagonist with high affinity for the human CXCR4 receptor in pre-clinical studies and is currently being investigated in metastatic breast cancer (mBC). Encouraging safety and efficacy data were previously published from a Phase 1 trial investigating B + eribulin (E) in patients (pts) with human epidermal growth factor receptor 2 negative (HER2-) mBC. Methods: In this multicenter, open-label trial, pts were randomized 1:1 to receive B (5.5 mg/kg) + E (1.4 mg/m2) or E alone. Eligible pts had HER2- locally advanced or mBC and had previously received 1−4 lines of chemotherapy in the advanced setting. Pts with hormonal receptor positive (HR+) disease must have received ≥1 line of endocrine therapy. The primary efficacy endpoints included objective response rate (ORR) and progression free survival (PFS) in the ≥3rd line population and PFS in the overall population. Overall survival (OS) was a key secondary endpoint. Results: 432 pts (aged 29-82 years) were enrolled with 348 treated in the ≥3rd line setting. Most pts (66.4%) were treated in the 3rd or 4th line, 96.1% had an Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1, and 35.6% had triple negative breast cancer. ORR and clinical benefit rate (CBR) data for the ≥3rd line population are presented in the table below. PFS and OS were not improved in the 3rd line population [mPFS 3.5 months (m) vs 4.0 m; hazard ratio 1.07 (96% CI: 0.81, 1.41); interim mOS 11.0 m vs 11.2 m hazard ratio 1.08 (99.9% CI: 0.66, 1.77)]. Results were consistent in the overall population and per investigator assessment.For the overall safety population, serious treatment-emergent adverse events (STEAEs) (28% versus 26.5%), treatment-emergent adverse events (TEAEs) leading to death (6.9% versus 6.4%) and TEAEs ≥Grade 3 (68.3% versus 64.2%) were broadly similar between the two arms. Infusion Related Reactions (IRR) were reported in 43.6% of patients treated with B + E. Conclusions: In this Phase 3 randomized trial, no differences in ORR, CBR, mPFS, or mOS were observed for B + E compared to E alone in any population of HER2-mBC patients. Efficacy parameters for E alone were similar to those reported previously. The combination was B + E was well-tolerated overall. ≥3rd Line Population(N=330)B + E(N=162)E(N=168)Objective Response Rate (95% CI)Per Independent Review Committee13.0% (8.2, 19.1)13.7% (8.9, 19.8)Per Investigator13.6% (8.7, 19.8)13.1% (8.4, 19.2)Clinical Benefit Rate (95% CI)Per Independent Review Committee16.7% (11.3, 23.3)19.6% (13.9, 26.5)Per Investigator21.6% (15.5, 28.7)21.4% (15.5, 28.4) Citation Format: Peter Kaufman, Miguel Martin, Ingrid Mayer, Linda Vahdat, Sonia Pernas, Peter Schmid, Heather McArthur, Rebecca Dent, Hope S Rugo, Carlos Barrios, Alexandra Bobirca, Francois Ringeisen, Daniela Schmitter, Javier Cortes. Balixafortide (a CXCR4 antagonist)+eribulin versus eribulin alone in patients with HER2 negative, locally recurrent or metastatic breast cancer: An international, randomized, phase 3 trial (FORTRESS) [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr PD13-01.

Trends in incidence, molecular diagnostics, and treatment of patients with breast cancer in Kazakhstan, 2014-2019

Relevance: Globocan reported 4,390 new breast cancer cases and 1,654 deaths from breast cancer in the Republic of Kazakhstan (RK) in 2020. Molecular diagnostics of breast cancer includes the determination of Hormone Receptor (HR), HER2, and Ki-67 status to detect patients
 with HR-positive tumors and administer effective treatment.
 Methods: This observational study included a retrospective analysis of incidence, molecular diagnostics, and treatment regimens in women with a confirmed breast cancer diagnosis aged 18 years old and older, registered in the RK Electronic Registry of Cancer Patients (ERCP) from 1 January 2014 till 31 December 2019.
 Results: In the study period (2014 to 2019), the number of breast cancer cases registered annually has doubled. The incidence increased by 46.9%. The share of locally advanced and advanced forms of breast cancer has decreased. The proportion of Luminal type A (HR+/HER2-)
 among newly diagnosed patients ranged from 17.9% to 30%. Chemotherapy and endocrine therapy with goserelin, buserelin, leuprorelin, and fulvestrant are standard first- and second-line treatments for HR+ breast cancer. Since fulvestrant indications have been expanded, more
 than 50% of patients with HR-positive advanced breast cancer receive fulvestrant as the first-line therapy.
 Conclusion: Breast cancer incidence growth and a decrease in the share of locally advanced and advanced breast cancer cases in the RK could be attributed to increased coverage of eligible women aged 40 to 70 with breast cancer mammographic screening. Although international guidelines support the administration of hormone therapy with or without targeted therapy in women with HR-positive, HER2-metastatic breast cancer, upfront use of chemotherapy remains common in the RK even in the absence of visceral crisis. The use of CDK4/6 inhibitor palbociclib in combination with hormone therapy has become routinely available since 2019