Two cases of melanomas paradoxically metastasizing to the intestinal tract during nivolumab therapy

We report two cases of melanomas in patients who developed intestinal metastasis despite other metastatic sites responding to nivolumab and despite the patients having favorable findings such as vitiligo and normal lactate dehydrogenase. The first case is an 85-year-old man who had been administrated nivolumab for lung/cutaneous metastases. After 22 courses of nivolumab therapy, fever and anorexia had appeared and his bodyweight had decreased. An intussusception on the ileocecal valve was revealed by computed tomography, and emergency surgery revealed metastatic lesions on the colon. The second case is an 87-year-old woman treated with nivolumab for lymph node metastases. After 10 courses, laboratory tests had revealed anemia and positive fecal occult blood. Her bodyweight had decreased. Capsule endoscopy showed scattered tumors and clots, indicating metastases of melanoma. The frequency of symptomatic intestinal metastasis of melanoma is very low. Further, intestinal metastasis of melanoma is difficult to detect through routine examinations. Our cases suggest that fecal occult blood test and decreased bodyweight are indications of intestinal metastases.