Collision nodal metastasis of bladder cancer and melanoma: The first reported case and literature review

Collision metastasis is a rare phenomenon of concomitant localization of 2 or more different tumors in the same lymph node. In most cases, primary malignancies are synchronous carcinomas arising in the same organ or area of the body. A 82-year-old man presented with hematuria and acute renal failure; he had undergone dermatological consultation ten months ago because of a large deep brown skin lesion in his dorso-lumbar region, which was not excised upon patient's request. He underwent radical cystectomy with extended pelvic lymphadenectomy due to nonpapillary high-grade urothelial carcinoma, with focal squamous features, infiltrating the bladder wall and prostate gland. In one left iliac lymph node, small foci of metastatic urothelial carcinoma (positive for P63 and CK34betaE12) were close to melanoma cells (positive for HMB45). The patient refused further treatment and died of metastatic disease 12 months after cystectomy. There is no specific clinical feature for nodal collision metastasis. A polymorphic histologic appearance poses the suspect, but immunohistochemical stains are needed to define the primary tumors. Collision metastases are thought to carry a poor prognosis. Their clinical relevance is linked to the fact that the patient faces 2 different metastatic tumors that may require specific multidisciplinary approach once diagnosed as metastatic. We present, to the best of our knowledge, the first case of collision nodal metastasis from bladder cancer and melanoma, and describe its clinical and histopathological characteristics to raise awareness on this rare occurrence, which portends a poorer prognosis than each single tumor.