Osimertinib for compound EGFR exon 19 deletion/T790M mutated lung squamous cell carcinoma.

The role of the epidermal growth factor receptor (EGFR) mutation status testing in lung squamous cell carcinoma (SqCC) remains controversial. Evidence of the effectiveness of osimertinib in SqCC with EGFR T790M mutation is limited. Here, we describe a hitherto unreported case of a stage III SqCC patient with compound mutation of EGFR exon 19 deletion (19Del) and T790M mutation. Pathological complete tumor response was achieved after treatment with osimertinib. We suggest that EGFR mutation testing should be performed in Asian patients who have not been definitively diagnosed with SqCC due to small lung biopsy samples. Osimertinib has shown good efficacy in SqCC harboring a "primary" resistance mechanism (EGFR T790M). KEY POINTS: An unreported case of stage III squamous cell carcinoma with synchronous occurrence of EGFR exon 19 deletion (19Del) and T790M mutation. Complete tumor response was achieved after treatment with osimertinib. EGFR mutation testing should be performed in Asian patients who are not definitively diagnosed with SqCC due to small lung biopsy samples. Osimertinib has shown good efficacy in SqCC harboring a "primary" resistance mechanism (EGFR T790M).