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 <.001). No evidence for a predictive impact of BRCA mutation on efficacy of 4xEC additional chemotherapy was seen overall or within pCR subgroups. Conclusions: Twelve weeks of neoadjuvant nab-pac/carbo is a highly effective anthracycline-free regimen that leads to an excellent pCR-rate of 64% in tumor BRCA1/2-mutated cases. BRC A1/2 mutation status could support this de-escalation strategy in early TNBC, but further prospective validation of survival impacts in larger cohorts and with longer follow up is needed. More detailed survival analyses will be presented at the meeting. Clinical trial information: NCT01815242.