EGFR and small cell lung carcinoma: Although it rarely happens this event determines a rapid disease deterioration and needs specific treatment.<h4>Patient and method</h4>We report a case of 75-year-old LUAD female with a p.L858R mutation in Epidermal Growth Factor Receptor (EGFR) who presented with SCLC transformation after responding to first line osimertinib treatment for only 6 months.