Cowden's syndrome is a rare autosomal dominant disorder that has been linked to germline mutations in the phosphatase and TENsin homolog (PTEN) gene. PTEN is a tumour suppressor gene that negatively regulates the PI3K-AKT-mTOR pathway. Cowden's syndrome is a multi-system disease with increased risks for a number of malignancies but very rarely for lung cancer. A systematic follow-up chest CT scan was performed to a 42 year's old female, light smoker. It showed a 20mm opacity of the left upper pulmonary lobe. Differential diagnose with benign tumours (such as hamartoma) was carefully searched. Procedures led to the diagnosis of a primitive lung adenocarcinoma. EGFR sequencing shows two rare somatic mutations (S768I and V769L). Lack of expression of PTEN is a non-sufficient condition leads to lung cancer formation alone. Nevertheless, it increases cell oncogenic potential. PTEN lacking in non small cell lung cancer is a frequent issue. It could be an alternative mechanism of non-efficacy of EGFR-TKI in cells with a sensitizing EGFR mutation. This case report, a very rare entity: a patient with a PTEN germline mutation and a lung adenocarcinoma harbouring two concomitant rare somatic mutations of EGFR. This observation comforts PTENs role in lung oncogenesis.
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