What happened, in summary

A 63-year-old woman with a 76 pack-year smoking history was diagnosed with Stage IIIB moderately differentiated squamous cell cancer of the left upper lung, classified as T2aN3M0. Testing showed PD-L1 expression of 60% and no EGFR mutation.

Her performance status was too poor for platinum-based chemotherapy. She received off-label pembrolizumab 200 mg every 3 weeks together with 66 Gy of radiation in 32 fractions. On day 48 of pembrolizumab, she was admitted with rapidly worsening breathlessness, dry cough, feverish symptoms, and very low oxygen levels.

The lung inflammation extended outside the radiation field. Antibiotics did not reverse the decline, and the clinical course supported pembrolizumab-related pneumonitis. The pneumonitis remained severe despite corticosteroids. She declined further immunosuppressive treatment and died from the treatment complication.