Stage IV Lung Adenocarcinoma With Delayed Pembrolizumab-Related Pneumonitis

What happened, in summary

A 77-year-old woman who had never smoked was evaluated for fatigue and found to have a large right lung mass with nodules in both lungs and enlarged mediastinal lymph nodes. Biopsy confirmed lung adenocarcinoma, and the disease was classified as Stage IV.

She started pemetrexed chemotherapy with pembrolizumab. After 6 cycles, the lung cancer and metastatic lesions gradually shrank, and she continued pembrolizumab alone as maintenance treatment. About 4 months later, the right lung lesion began to grow. Pemetrexed was restarted, but the disease continued to progress after 3 additional cycles.

Her family chose local iodine-125 seed brachytherapy, while pembrolizumab was continued. The tumor began shrinking again. A CT scan 1 year later showed a smaller right hilar lesion and otherwise stable disease. Pembrolizumab was stopped after about 2 years of treatment.

Two and a half months later, she developed fever, cough and shortness of breath. Infection and cancer progression were investigated, but lung biopsy showed organizing pneumonia without tumor cells. She was diagnosed with pembrolizumab-related pneumonitis and improved with steroid treatment and intravenous immunoglobulin. At the latest follow-up, the pneumonitis symptoms had resolved.