Abstract

e12637 Background: Our previous study suggested that HER2-positive breast cancer patients with activated mutations in PIK3CA are less likely to achieve a pathological complete response (pCR) from pyrotinib combined with trastuzumab in the neoadjuvant setting. The relationship of PIK3CA mutations and survival remains unknown. Methods: The genomic characteristics of 425 cancer-related genes from the archived tumour blocks of 50 patients enrolled in a prospective neoadjuvant pyrotinib and trastuzumab plus chemotherapy clinical trial (ChiCTR1900022293) were assessed by next-generation sequencing (NGS). The relationship between PIK3CA mutations and event-free survival (EFS) and overall survival (OS) were explored. Results: Among the cohort of 50 cases, five patients dropped out during treatment due to various reasons, whereas the other 45 patients were followed up until August 31, 2023. The median follow-up was 36.1 months, and mEFS and mOS were not reached yet. Kaplan-Meier estimated 3-year EFS rate and OS rate were 91.1% (95% confidence interval [CI]=83.2%-99.8%) and 97.1% (95% CI=91.8%-100%), respectively. Patients with wild-type PIK3CA tended to achieve a better 3-year EFS rate (96.2% vs 63.2%, hazard ratio [HR]=0.18, 95% CI=0.02-1.59, log-rank P = 0.081) compared with the patients with mutated PIK3CA. Besides, patients with pCR showed a better 3-year EFS rate (96.2% vs 84.2%, HR=0.16,95% CI=0.02-1.45, log-rank P = 0.063) compared with the patients without pCR. Conclusions: HER2-positive breast cancer patients with activated mutations in PIK3CA are less likely to benefit from pyrotinib combined with trastuzumab in the neoadjuvant setting, but this conclusion still needs to be confirmed by large-sample studies and long-term follow-up results. Clinical trial information: 1900022293.