What happened, in summary

A 78-year-old man with EGFR-mutated lung cancer received osimertinib for 14 months. When the disease progressed, the tumor had transformed into small cell lung cancer. Review of the original diagnostic specimen identified a TP53 p.Y220C alteration. After the small cell transformation was identified, he did not begin another anticancer regimen and instead received palliative care. He died 1 month later. His course was the shortest of the four transformed cases and shows how rapidly a lung cancer can worsen once resistance and a major change in tumor type occur during targeted treatment.