SMAD4 Mutation in Small Cell Transformation of Epidermal Growth Factor Receptor Mutated Lung Adenocarcinoma

AbstractThe large screening of exons 18 to 21 of the epidermal growth factor receptor (EGFR) gene may lead to the discovery of rare, atypical molecular alterations for which the sensitivity to tyrosine kinase inhibitors (TKIs) remains uncertain. We are reporting a rare exon 18 EGFR mutation (p.E709_710 > D) that confers sensitivity to second‐generation EGFR TKI (afatinib), lasting for 1 year. Tumor progression biopsy showed small cell lung cancer transformation, associated with a SMAD4 mutation.Key Points. A rare exon 18 epidermal growth factor receptor mutation with sensitivity to afatinib is reported.Small cell transformation was observed at tumor progression.Acquisition of a SMAD4 mutation was observed at tumor progression.

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