Psoriatic arthritis complicating lung cancer.

Psoriatic arthritis is an inflammatory arthritis associated with psoriasis. While an elevated incidence of lung cancer has been observed in patients with RA or psoriasis, there has been no report of psoriatic arthritis associated with lung cancer. We here report the first case of psoriatic arthritis which developed lung cancer. In this case, it was suspected that a combination of cigarette smoking, pulmonary fibrosis, and low-dose methotrexate therapy might have promoted the development of lung cancer.