Non-small cell lung carcinomas with CTNNB1 (beta-catenin) mutations: A clinicopathological study of 26 cases

Beta-catenin, encoded by the CTNNB1 gene, plays an important role in cell proliferation. Mutations of CTNNB1 are oncogenic in several tumor types and are often associated with a nuclear abnormal expression. However, such mutations have only rarely been reported in non-small cell lung carcinomas and their clinical signification is not well described. Our study was conducted on 26 CTNNB1-mutated non-small cell lung carcinomas. Tumors were routinely tested by next generation sequencing for mutations in exon 3 of CTNNB1 gene. Twenty three cases were from a series of 925 tumors (2.48%). The hospital files and pathological data, from surgical samples (n = 16), small biopsies (n = 5) and trans-bronchial fine needle aspirations (n = 5), were reviewed. Immunohistochemistry was performed with an anti-beta-catenin antibody. There were 10 female and 16 male patients aged 52 to 83. Eleven of 25 patients were no-smoking or light smokers. Three cases were diagnosed while under treatment with EGFR tyrosine kinase inhibitor. There were 25 adenocarcinomas and 1 squamous cell carcinoma. Most adenocarcinomas had a papillary component and were TTF1-positive. One case was a well-differentiated fetal adenocarcinoma. Eleven cases (42%) with CTNNB1 mutations showed associated EGFR mutations. The frequency of CTNNB1 mutations was higher among EGFR mutated carcinomas. Immunohistochemistry showed heterogeneous nuclear or cytoplasmic abnormal expression. Our study shows that CTNNB1 mutations mostly occur in TTF1-positive adenocarcinomas with a papillary pattern. These mutations are often associated with EGFR mutations and possibly interfer in the mechanism of resistance to tyrosine kinase inhibitors. Our experience suggests that immuno-histochemistry cannot be used for screening.