A case of polyarteritis nodosa complicated by rectal cancer.

Solid cancers are rarely complicated by the occurrence of polyarteritis nodosa (PN), and most cases diagnosed as PN are, in fact, cases of paraneoplastic vasculitis. Paraneoplastic vasculitis is usually resolved after tumor removal. We present a rare case of a 69-year-old man with PN complicated by rectal cancer, without the occurrence of paraneoplastic vasculitis. Microscopic examination of the resected cancer lesion revealed inflammation of some arteries and neutrophil and lymphocyte infiltration, fibrin deposition, stenosis, and vasodilatation of capillaries caused by congestion in the submucosal layer. It was unclear how these findings exerted influence on the rectal cancer. Although the symptoms of PN did not improve after the patient's tumor was removed surgically, the symptoms improved rapidly after oral treatment with prednisolone and cyclophosphamide.