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Objective: To analyze the mutation status of the PIK3CA gene and the clinicopathological characteristics in lung adenocarcinoma. Methods: Lung adenocarcinoma cases that underwent next-generation sequencing (NGS) for the PIK3CA gene at the Department of Pathology, the Third People's Hospital of Henan Province and the Henan Provincial People's Hospital from January 1, 2020 to December 31, 2024 were collected. Clinicopathological indicators were recorded for statistical analysis, and follow-up was conducted. Results: A total of 127 lung adenocarcinoma patients with PIK3CA mutations were detected. There was a slight female predominance (75/127, 59.1%), the majority were non-smokers (95/127, 74.8%), and age was 65.0(57.0, 71.0)years old. Most lung adenocarcinomas were moderately differentiated (56/127, 44.1%) or poorly differentiated (44/127, 34.6%), with clinical stage Ⅳ being the most common (60/127, 47.2%). Hotspot mutations in the PIK3CA gene were present in 77 cases (77/127, 60.6%), specifically manifesting as mutations in exon 9 (E9, p.E545K/Q, p.E542K) and exon 20 (E20, p.H1047R/L/Y). Compared with E9 mutations, E20 mutations were more frequently associated with lymph node metastasis, visceral pleural invasion, airspace dissemination, poorer differentiation, and higher staging, and had a worse prognosis. Multivariate Cox analysis showed that PIK3CA hotspot mutations did not significantly affect prognosis (HR=0.586,95%CI=0.343-1.002,P=0.051). Co-existing mutations in other genes were found in 105 cases (105/127, 82.7%), with 72 cases (72/105, 56.7%) harboring concomitant EGFR mutations. Of the 62 cases receiving targeted therapy, 11 developed drug resistance, primarily due to secondary EGFR exon 20 mutations (9/11). Conclusions: Lung adenocarcinomas with PIK3CA mutations exhibit distinct clinicopathological characteristics in terms of gender, age, smoking history, differentiation degree, and clinical stage. Acquired drug resistance in lung adenocarcinoma may be accompanied by PIK3CA mutations, but PIK3CA mutation is not the main mechanism of targeted therapy resistance in lung adenocarcinoma patients.