Abstract 236P
Background
First-line treatment of metastatic breast cancer (mBC) consists of the combination of CDK4/6i & ET, regardless of histoype. Most pts enrolled in clinical trials had ductal mBC, with limited data on CDK4/6i in mLBC. This study aims to analyze the survival outcomes of pts with mLBC treated with CDK4/6i, compared to pts with non-lobular mBC.
Methods
In this retrospective study, we included pts with hormone receptor-positive/HER2-negative mBC treated with CDK4/6i (Jan 2016 to Jan 2024). We estimated the median progression-free survival (mPFS) and overall survival (mOS) by Kaplan-Meier and compared by log-rank test and Cox models (significance at p-value<0.05).
Results
210 pts were identified, 42 had mLBC. Baseline characteristics are reported in the table. At a median follow-up of 53.6 months (95% Confidence Interval [CI], 45.1-62.1), mPFS was 16.7 months (95% CI, 12.9-20.4) and mOS 46.8 months (95% CI, 38.8-55.2), with no differences for pts with mLBC compared to those with non-lobular mBC (PFS, p=0.45; OS, p=0.83), even after adjusting for all baseline characteristics (Hazard Ratio [HR] PFS: 1.1 [95% CI, 0.7-16]; HR OS: 0.9 [95% CI, 0.5-1.5]). Table: 236P
| Characteristic | All (N=210) | Lobular (N=42) | Non-lobular§ (N=168) | P |
| Age, median (IQR) | 57 (49-66) | 62 (55-67) | 56 (49-65) | .01 |
| Luminal A-like*, n (%) | 62 (30) | 16 (38) | 46 (27) | .17 |
| De novo M1, n (%) | 55 (26) | 9 (21) | 46 (27) | .43 |
| (Neo)adjuvant CT, n (%) | 78 (37) | 12 (28) | 66 (39) | .19 |
| Previous CT for M1, n (%) | 56 (26) | 5 (12) | 51 (30) | .02 |
| ET Sensitive | Resistant**, n (%) | 96 (45) | 114 (55) | 16 (28) | 26 (61) | 80 (48) | 88 (52) | .26 |
| Line of CDK4/6i, median (IQR) | 1 (1-2) | 1 (1-2) | 1 (1-2) | .06 |
| Palbociclib | Abemaciclib| Ribociclib, n (%) | 150 (72) | 18 (8) | 42 (20) | 33 (78) | 2 (5) | 7 (17) | 117 (70) | 16 (10) | 35 (21) | .45 |
| ORR, % (95% CI) | 31 (25-38) | 38 (21-52) | 30 (23-37) | .45 |
| mPFS, month | 16.7 | 17.1 | 16.1 | .45 |
| mOS, month | 46.8 | 45.5 | 47.6 | .83 |
§ Including ductal and other histotype *PgR³20%, Ki67<20% and grade 1-2. **ESMO-ABC criteria.Legend: CT, chemotherapy; IQR, interquartile range; M1, metastatic; n, number; ORR, objective response rate.
Conclusions
In this study, we report that pts with mLBC derive no dissimilar benefits from CDK4/6i compared to those with non-lobular mBC.
Legal entity responsible for the study
The authors.
Funding
Has not received any funding.
Disclosure
D. Trapani: Other, EMA Healthcare Professional Working Party (HCPWP), member: European Medicines Agency (EMA); Other, EML Cancer Medicines Working Group (CMWG), member: World Health Organization (WHO); Other, Strategic Advisory Group of Experts on In Vitro Diagnostics (SAGE IVD), chair: World Health Organization (WHO). A. Marra: Financial Interests, Personal, Advisory Board: Menarini/Stemline; Financial Interests, Personal, Invited Speaker: Roche; Financial Interests, Personal, Other, Travel Support: AstraZeneca. C. Criscitiello: Financial Interests, Personal, Invited Speaker: Pfizer, Novartis, Eli Lilly, Roche, Gilead; Financial Interests, Personal, Advisory Board: MSD, Seagen, AstraZeneca, Daiichi Sankyo. G. Curigliano: Financial Interests, Personal, Invited Speaker: Roche, AstraZeneca, Daiichi Sankyo, Novartis, Pfizer, Pfizer; Financial Interests, Personal, Advisory Board: Roche, AstraZeneca, Daiichi Sankyo, Lilly, Pfizer, Veracyte, BMS, Merck, Exact Sciences, Celcuity; Financial Interests, Personal, Advisory Board, Advisory Board: Menarini, Gilead; Financial Interests, Personal, Other, Advisory Board: Ellipsis; Financial Interests, Institutional, Research Grant, Investigator Initiated Trial: Merck; Financial Interests, Institutional, Funding, Phase I studies: BMS, Novartis, AstraZeneca, Daiichi Sankyo, Roche, Blueprint Medicine, Kymab, Astellas, Sanofi, Philogen; Financial Interests, Institutional, Invited Speaker, Phase I clinical basket trial: Relay Therapeutics; Non-Financial Interests, Officer, Italian National Health Council as Advisor for Ministry of Health: Consiglio Superiore di Sanità; Non-Financial Interests, Advisory Role, Member of the Scientific Council. Patient advocacy association: Europa Donna; Non-Financial Interests, Advisory Role, Cancer Research Foundation: Fondazione Beretta; Non-Financial Interests, Member of Board of Directors, No compensation for this role. This a public national company for cancer prevention: Lega Italiana Lotta ai Tumori; Non-Financial Interests, Officer, Member of the Advisory Council: EUSOMA; Non-Financial Interests, Officer, ESMO Clinical Practice Guidelines Chair: ESMO; Non-Financial Interests, Member of Board of Directors, Chair of Clinical Practice Guidelines Committee: ESMO. E. Munzone: Financial Interests, Personal, Advisory Board: Daiichi Sankyo/AstraZeneca, Eisai, Exact Science, MSD Oncology, Pfizer, Seagen. All other authors have declared no conflicts of interest.