Clinico-pathological Features of PIK3CA Mutation in HER2-Positive Breast Cancer of Indian Population.

PIK3CA pathway is one of the important signaling pathways in cells, which is involved in cell proliferation, cell survival, motility, and growth. Mutation in PIK3CA gene negatively effects to anti-HER2 therapy in breast cancer patients. PIK3CA gene of HER2-positive breast cancers associated with reduced sensitivity to neoadjuvant therapy. In this study, we assessed the frequency of PIK3CA mutations and influence of PIK3CA mutations on patient survival in a series of HER2-positive breast cancer patients. PIK3CA mutations were assessed by pyrosequencing and next generation sequencing in 107 HER2-positive breast cancer patients of a tertiary Cancer Centre of India from Jan 2012 to Jun 2013 with minimum follow-up of 3 years. We found PIK3CA mutations in 26 tumors (24.2%) of which 5 were in exon 9, 20 were in exon 20, and 1 was in both exon 9 and 20. In exon 9, the mutation c.1634A>G was found in 4 cases and mutation c.1636C>A was found in 2 cases. In exon 20, the mutation c.3140A>G was found in 15 cases and c.3140A>T was found in 6 cases. The outcome between PIK3CA mutated versus PIK3CA wild type was significant showing p value 0.014. Overall survival of mutation and treatment with herceptin, mutation with other chemotherapy treatment in both early breast cancer (EBC), and locally advanced breast cancer (LABC) showed significant p value 0.037 and 0.044 respectively. In conclusion, we identified 24.2% somatic mutation of PIK3CA in HER2-positive breast cancer patients. PIK3CA mutation is significantly associated with ER-positive tumors. The frequency and distribution pattern reported in this study is similar to the global report. Overall survival of PIK3CA mutation is slightly lower but in patients who received herceptin with PIK3CA mutation showed better clinical outcome.