225P Platinum-based chemotherapy and PARP Inhibitors for BRCA mutated metastatic breast cancer (LATER-BC): Retrospective multicentre analysis of post-progression treatments

Patients (pts) with germinal BRCA mutated (gBRCAm) breast cancer (BC) have an enhanced sensitivity to platinum-based chemotherapy (PBC) and PARP-inhibitors (PARPi). As reported in ovarian cancer, resistance these treatments partially overlap. In gBRCAm BC, it is unclear if prior exposure PARPi/PBC affects tumor response subsequent PBC/PARPi. We conducted a retrospective, multicentre observational study assess the benefit of PARPi post-PBC viceversa pts BC. Pts included received: (neo)adjuvant PBC then advanced setting (group [Gr] 1); followed by (Gr2), or (Gr3) setting. median progression free survival (mPFS) disease control rate (DCR) for each group. Correlative analyses were provided (significance at p<0.05). 59 from 5 centers included. characteristics outcomes are table. PARPi-mPFS metastatic Gr1 (N=9) was 4.8 months (mo). DCR 67%. Gr2 (N=31), mPFS 4.3 4.5 mo; DCRs 97% 45%. Age<46 platinum interval (PFI)>6mo associated longer PARPi-PFS (p=.009 .016). PBC-PFS>6mo PFI>6mo PARPi-DCR (p=.031 .032). Gr3 (N=21) 5.0 1.8 mo PBC, 67 14%. earlier lines (1-2) PBC-PFS (p=.020). PARPi-PFS>9mo PARPi-FI>6mo PBC-DCR (p=.015 .026). Table: 225PPts outcomesGr1 (N=9)Gr2 (N=31)Gr3 (N=21)Age diagnosis – (range)38 (29-62)40 (28-72)39 (28-62)Visceral %67%81%86%De novo %0%13%24%BRCA1/BRCA2/NA %56/44/0%48/39/13%29/62/10%TNBC/Luminal-like %67/33%52/48%33/67%PARP line (1-2/>2) %67/33%29/71%5/95%NA-PBCPARPi post-NA-PBCPBCPARPi post-PBCPARPiPBC post-PARPiN. (range)NA2 (2-5)2 (1-10)3 (2-12)3 (1-11)4 (2-13)PFS (range)NA4.8 (0.9-25.4)4.3 (1.5-23.8)4.5 (0.3-35.7)5.0 (0.9-12.4)1.8 (0.1-5.0)DCR %NA67%97%45%67%14%NA: not applicable; (NA)-PBC: (neoadjuvant) chemotherapy; TNBC: triple negative BC Open table new tab NA: Sensitivity overlap on PBC/PARPi PFI/PARPi-FI represent two potential predictive factors treatment PARPi/PBC.