An analysis of PIK3CA hotspot mutations and response to neoadjuvant therapy in breast cancer patients from four prospective clinical trials.

The PI3K signaling pathway is frequently dysregulated in breast cancer (BC), and mutations in PIK3CA, are relevant for therapy resistance in HER2pos BC. Mutations in exons 9 or exon 20 may have different impact on response to neoadjuvant chemotherapy-based treatment regimens. We investigated PIK3CA mutations in 1691 early BC patients, randomized in four neoadjuvant multicenter trials: GeparQuattro (NCT00288002), GeparQuinto (NCT00567554), GeparSixto (NCT01426880) and GeparSepto (NCT01583426). The role of different PIK3CA exons and hotspots for pathological complete response (pCR) after neoadjuvant chemotherapy (NACT) and patient survival was evaluated for distinct molecular subgroups and anti-HER2 treatment procedures. A total of 302 patients (17.9%) of the full cohort of 1691 patients had a tumor with a PIK3CA mutation, with a different prevalence in molecular subgroups: luminal/HER2neg 95 of 404 patients (23.5%), HER2pos 170 of 819 patients (20.8%) and TNBC 37 of 431 patients (7.9%). We identified mutations in PIK3CA exon 20 to be linked with worse response to anti-HER2 treatment (OR=0.507, 95%CI 0.320-0.802, p=0.004), especially in HR positive HER2 positive BC (OR=0.445, 95%CI 0.237-0.837, p=0.012). In contrast, exon 9 hotspot mutations p.E452K and p.E545K revealed no noteworthy differences in response therapy response. Luminal/HER2neg patients show a trend to have worse treatment response when PIK3CA was mutated. Interestingly, patients with residual disease after neoadjuvant treatment, have better survival when PIK3CA was mutated. PIK3CA hotspot mutation p.H1047R are associated with worse pCR rates after NACT in HER2pos BC, while hotspot mutations in exon 9 seems to have less impact.