Lung cancer remission after pembrolizumab despite severe inflammatory arthritis

What happened, in summary

A 56-year-old man developed right-sided numbness while on holiday in January 2018. Brain imaging identified cancerous lesions, and further testing found a right-lung non-small cell adenocarcinoma with temporal and parietal brain metastases. The tumor was PD-L1-positive. He received radiotherapy to the brain lesions and right lung in early March, then began pembrolizumab in May 2018. The cancer responded completely.

About six months after starting pembrolizumab, he developed severe swelling and pain in both knees and the small joints of his hands, later involving his elbows. At times he could not walk. Because the cancer had already achieved a complete response and the immune-related symptoms were severe, pembrolizumab was stopped. Etoricoxib, methotrexate, sulfasalazine, and prednisolone brought little relief. A knee biopsy supported inflammatory arthritis.

He then consented to off-label tofacitinib 5 mg twice daily. Joint redness and swelling decreased rapidly, muscle strength improved, and within two weeks the clinical response was dramatic. He reached complete arthritis remission by week 20 and remained in sustained remission for 24 months. Methotrexate was substantially reduced while tofacitinib continued.

At 28 months from the lung-cancer diagnosis, the adenocarcinoma remained in complete remission. He had received no further cancer treatment since mid-2019. Movement returned, he could walk without an aid, and he resumed exercise, work, and daily life with his wife.