Lack of response to nivolumab in a patient with EGFR-mutant non-small cell lung cancer adenocarcinoma sub-type transformed to small cell lung cancer

•A rare case of EGFR-mutant NSCLC transformed to SCLC treated with nivolumab chemotherapy.•PD-L1 expression was 0% in transformed tumour cells.•No response to nivolumab was observed in this rare transformed tumour.

Small cell transformation is a rare but well recognised mechanism of acquired resistance to EGFR-TKI therapy in EGFR-mutated NSCLC, but optimal drug therapy thereof is unknown. Nivolumab has demonstrated activity in relapsed de novo small cell lung cancer in early phase trials. Here, we report a case of transformed EGFR-mutant SCLC treated with nivolumab with no benefit.