Complete response to pembrolizumab despite treatment-related lung inflammation

What happened, in summary

A 45-year-old man presented in 2024 with coughing up blood and chest pain. Imaging showed lung adenocarcinoma with pleural spread and involvement of a rib, making the disease Stage IV. The tumor had high PD-L1 expression at 70%, with no driver alteration identified on genomic testing.

He started pembrolizumab and also received palliative radiation to the painful rib lesion. By January 2025, imaging showed a complete metabolic response. Soon afterward, he developed fever and cough with lung inflammation inside the previous radiation area. Pembrolizumab was paused while he received corticosteroids.

Treatment was later restarted, but during steroid tapering he again developed cough, fever, and shortness of breath. New lung changes appeared outside the radiation field. Bronchoscopy and biopsy supported organizing pneumonia rather than infection or cancer progression. Pembrolizumab was stopped again, and a longer course of corticosteroids led to marked improvement.

By November 2025, the lung inflammation had nearly completely resolved. Serial imaging continued to show a complete cancer response without evidence of progression, and he remained under close surveillance.