PIK3CA Mutations Are Associated With Lower Rates of Pathologic Complete Response to Anti–Human Epidermal Growth Factor Receptor 2 (HER2) Therapy in Primary HER2-Overexpressing Breast Cancer

PURPOSE: Phosphatidylinositol 3-kinase (PI3K)/AKT pathway aberrations are common in breast cancer, with mutations in PIK3CA being the most common. This study investigated the association between PIK3CA genotype and pathologic complete response (pCR) rates in human epidermal growth factor receptor 2 (HER2)-positive breast cancer treated with either dual or single anti-HER2 treatment in addition to neoadjuvant chemotherapy. PATIENTS AND METHODS: PIK3CA mutations in 504 tumor samples from participants in the neoadjuvant GeparQuattro, GeparQuinto, and GeparSixto studies were evaluated. All HER2-positive patients received either trastuzumab or lapatinib or the combination plus anthracycline-taxane chemotherapy. PIK3CA mutations were evaluated in formalin-fixed, paraffin-embedded tissues from core biopsies with a tumor cell content of ≥ 20% by using classical Sanger sequencing of exon 9 and exon 20. RESULTS: Overall, 21.4% of the patients harbored a PIK3CA mutation. Detection of a PIK3CA mutation was significantly associated with a lower pCR rate (19.4% with PIK3CA mutation v 32.8% with PIK3CA wild-type; odds ratio OR, 0.49; 95% CI, 0.29 to 0.83; P = .008). In the 291 hormone receptor (HR) -positive tumors, pCR rate was 11.3% with a PIK3CA mutation compared with 27.5% with PIK3CA wild-type (OR, 0.34; 95% CI, 0.15 to 0.78; P = .011). In 213 patients with HR-negative tumors, pCR rate was 30.4% with PIK3CA mutation and 40.1% without (OR, 0.65; 95% CI, 0.32 to 1.32; P = .233; interaction test P = .292). In multivariable analysis, HR status and PIK3CA status provided independent predictive information. In patients with PIK3CA mutation, the pCR rates were 16%, 24.3%, and 17.4% with lapatinib, trastuzumab, and the combination, respectively (P = .654) and in the wild-type group, they were 18.2%, 33.%, and 37.1%, respectively (P = .017). Disease-free survival and overall survival were not statistically significantly different between patients with mutant and wild-type PIK3CA. CONCLUSION: HER2-positive breast carcinomas with a PIK3CA mutation are less likely to achieve a pCR after neoadjuvant anthracycline-taxane-based chemotherapy plus anti-HER2 treatment, even if a dual anti-HER2 treatment is given.