Pathological complete response rate and survival in patients with BRCA-associated triple-negative breast cancer after 12 weeks of de-escalated neoadjuvant chemotherapy: Translational results of the WSG-ADAPT TN randomized phase II trial (NCT01815242)

579 Background: The phase II trial WSG-ADAPT TN randomized triple-negative breast cancer (TNBC) patients to receive 12 weeks of neoadjuvant nab-paclitaxel (nab-pac) combined with carboplatin (carbo) vs gemcitabine (gem) and showed a substantial improvement of pathological complete response (pCR: ypT0/is, ypN0) with carbo (45.9% vs 28.7%). pCR had a strong favorable impact on iDFS after 3-year follow-up. Distribution of tumor mutations in BC-associated genes and impact of BRCA mutation status on pCR and outcome are analyzed here. Methods: NGS-based mutational analysis of BRCA1/2 and 18 further (potentially) BC-associated genes was performed on DNA derived from pretreatment FFPE samples (gem: n = 158, carbo: n = 108) using a customized gene panel. Variants with a variant fraction of ≥5% were included and classified according to IARC and ENIGMA guidelines. Results: In 42 of the 266 analyzed samples, at least one deleterious BRCA1/2-variant was found (15.8%; BRCA1 n = 37, BRCA2 n = 3, BRCA1+ BRCA2 n = 2) one of which displayed an additional STK11-mutation. In the BRCA1/2-negative cohort, a mutation in one of 14 further analyzed (potential) BC-risk genes was found in 19 samples (7.1%; BARD1 n = 3, CHEK2 n = 2, CDH1 n = 2, FANCM n = 3, PALB2 n = 5, RAD50 n = 1, RAD51C n = 1, RAD51D n = 1, XRCC2 n = 1; no deleterious mutations were found in ATM, BRIP1, MRE11A, NBN). At least one deleterious variant in TP53, PIK3CA, PTEN or MAP3K1 was seen in 89.1% (n = 237; TP53 n = 233, PIK3CA n = 22 PTEN n = 15, MAP3K1 n = 1). In 22 samples (8.3%) no deleterious mutation was identified in the analyzed genes. Overall, patients with tumor BRCA mutation (carbo n = 14, gem n = 28) had 45.2% vs 34.4% pCR (OR = 1.58, 95%-CI: 0.81-3.07, p =.18) without a mutation. pCR in the small group with mutation receiving carbo (n = 14) was 64.3% vs. 34.5% in all others (OR = 3.41, 95%-CI: 1.11-10.50; p =.03); direct comparison to BRCA-positive patients receiving gem (n = 28, 35.7%, OR = 3.2, 95%-CI: 0.85-12.36, p = 0.079) did not reach statistical significance. The results suggest that the strong favorable impact of pCR on iDFS is preserved even among BRCA-positive patients (n = 42, p =.07), as well as in the BRCA-negative subgroup (p