Abstract 224P
Background
Endocrine therapy (ET)-sensitive mILC responds well to first-line AI in combination with CDK4/6is. Recent studies have assessed the efficacy of single agent oral selective estrogen receptor degrader (SERD) in comparison to FUL post exposure to AI plus CDK4/6is revealing markedly reduced median progression-free survival (mPFS) in the FUL arm of approximately 2 months. This showcases an area of unmet need for patients post exposure to AI plus CDK4/6is. The impact of histology was not examined and could have important clinical implications. Establishing a historical control dataset for single-agent FUL can be hypothesis generating, offering valuable insights that may inform the design of future ILC-specific studies.
Methods
In an observational, single-institution investigation using data from the MD Anderson breast cancer prospectively collected electronic database, we searched for patients with a diagnosis of HR+ HER2-negative mILC who received second-line FUL following AI plus CDK4/6is. The method of Kaplan and Meier was used to estimate the distribution of overall survival (OS) and PFS.
Results
We reviewed 369 mILC patients, of whom 25 received single agent FUL and were included in the final analysis. Patient characteristics showed a median age of 60, 85% were non-Hispanic, 90% were White; all had ER positive tumors, 70% were PR positive, and 60% were HER2-low. 80% of the patients received prior palbociclib with 15% receiving ribociclib, and 5% receiving abemaciclib. The mPFS was 2.2 months with 95% confidence interval (CI) [1.8 – 4.5], and a 6-month PFS of 17.7%. The mOS was 10.4 months with 95% CI [7.5 – 15.4], and a 12-month OS of 44.3%.
Conclusions
This is the only analysis to date to report outcomes of second-line single agent FUL in mILC patients exposed to AI plus CDK4/6is. Our findings underscore the urgent need for exploring novel therapeutic approaches and combinations in this patient population to improve outcomes in mILC. These results serve as an important historical controls for informing the design and development of future studies tailored specifically to address the unique challenges posed by mILC.
Legal entity responsible for the study
MD Anderson Cancer Center.
Funding
Has not received any funding.
Disclosure
J.A. Mouabbi: Financial Interests, Personal, Invited Speaker: BostonGene; Financial Interests, Personal, Advisory Board: AstraZeneca, Novartis, Gilead; Financial Interests, Institutional, Invited Speaker: BMS. F. Meric-Bernstam: Financial Interests, Personal, Other, Consultant: AstraZeneca, F. Hoffman-La Roche Ltd., Zymeworks, OnCusp Therapeutics; Financial Interests, Personal, Advisory Board, Advisory Board/Consultant: Seagen; Financial Interests, Personal, Advisory Board: Zentalis, Karyopharm, Biovica, Eisai, Protai, TheraTechnologies; Financial Interests, Personal, Other, Consulting: Tallac Therapeutics, Lengo Therapeutics, LOXO-Oncology, Black Diamond, Infinity Pharmaceuticals, AbbVie, GT Aperion, Ecor1; Financial Interests, Personal, Other, Consutling: Menarini Group; Financial Interests, Institutional, Other, Local PI / Research Grant: Aileron Therapeutics, Bayer Healthcare, CytomX Therapeutics Inc., Daiichi Sankyo Ltd., eFFECTOR Therapeutics, Taiho Pharmaceutical Co.; Financial Interests, Institutional, Other, Local PI / Research Grant / Coordinating PI: AstraZeneca; Financial Interests, Institutional, Invited Speaker: Calithera Biosciences, Curis Inc., Debiopharm International, Guardant Health Inc., Klus Pharma, Novartis; Financial Interests, Institutional, Other, Local PI / Steering Committee Member: Genentech Inc.; Financial Interests, Institutional, Research Grant: Takeda Pharmaceutical Co., Puma Biotechnology Inc., Repare; Other, Travel support: European Organisation for Research and Treatment of Cancer (EORTC), European Society for Medical Oncology (ESMO); Other, Travel Support: Cholangiocarcinoma Foundation. D. Tripathy: Financial Interests, Personal, Advisory Board, Serving on Steering Committee for TrialsEducational Lectures: Novartis; Financial Interests, Personal, Advisory Board, Steering Committee for and ongoing trial: Pfizer; Financial Interests, Personal, Advisory Board, Advisory council for design and interpretation of trials: GSK; Financial Interests, Personal, Invited Speaker, Educational Lectures: AstraZeneca; Financial Interests, Personal, Advisory Board, To discuss and interpret clinical trial data: Immunomedics; Financial Interests, Personal, Advisory Board, Advice on clinical trial design: OncoPep; Financial Interests, Personal, Invited Speaker, Lecture on gene profiling: Exact Sciences; Financial Interests, Personal, Advisory Board, Consulting: Sermonix; Financial Interests, Personal, Advisory Board, Consultant: Personalis, Puma Biotechnology, Roche, AMBRX, BeiGene; Financial Interests, Personal, Advisory Board, Consultant and service on Data Monitoring Committee: Gilead; Financial Interests, Institutional, Research Grant, Funding for laboratory experiments on the inhibition of CXCR4 in breast cancer cells: Polyphor; Financial Interests, Institutional, Invited Speaker, Global PI on one trial and local PI on another trial: Novartis; Financial Interests, Institutional, Invited Speaker, Payment to institution for clinical trial expenses: AMBRX. R. Layman: Financial Interests, Personal, Advisory Board: Eli Lilly, Novartis, Celcuity, Gilead Sciences, BioTheryx; Financial Interests, Personal, Invited Speaker: Pfizer, Pfizer, Eli Lilly, Celcuity; Financial Interests, Institutional, Invited Speaker: Accutar Biotechnology, Eli Lilly, Pfizer, Celcuity, Arvinas; Financial Interests, Institutional, Research Grant, Supply of drug for clinical trial: Novartis, Puma; Financial Interests, Institutional, Research Grant: Celcuity. All other authors have declared no conflicts of interest.