Long-term lung cancer response complicated by immune-related lung inflammation

What happened, in summary

A 40-year-old woman was diagnosed in 2019 with Stage IV lung adenocarcinoma that had spread to several areas, including the pleura, bone, peritoneum, lungs, and brain. Testing found a KRAS G12A mutation and high PD-L1 expression at 90%.

She began pembrolizumab, but the cancer progressed after the first cycle. Chemotherapy was then added to pembrolizumab, producing a rapid response, and she continued long-term pembrolizumab maintenance. In 2023, a single brain metastasis was treated with stereotactic radiation and responded completely.

After more than 5 years of pembrolizumab, scans showed new lung inflammation while the cancer itself remained controlled. She later developed cough, fever, and shortness of breath. Bronchoscopy and biopsy supported organizing pneumonia rather than cancer progression or infection. Pembrolizumab was stopped, and corticosteroid treatment led to rapid improvement.

By October 2025, imaging showed complete resolution of the lung inflammation. She remained active with an ECOG performance status of 0 and continued to have systemic and intracranial remission.