Bladder metastasis of cutaneous melanoma in the differential diagnosis of urothelial carcinoma

Abstract

Cutaneous melanoma is an extremely aggressive neoplasm with a marked tendency for hematogenous dissemination. Although the most frequent metastatic sites include the lung, liver, brain, and bone, bladder involvement is exceptional and rarely presents clinically overt. The clinical and imaging similarity to primary urothelial carcinoma represents a significant diagnostic challenge. We report the case of a 78-year-old man with a history of stage IIC (pT4b) cutaneous melanoma treated with surgical resection and adjuvant radiotherapy, who presented with gross hematuria. Computed tomography urography revealed a solid, pedunculated bladder mass with contrast enhancement, initially interpreted as primary urothelial carcinoma. Transurethral resection of the lesion was performed. Histopathological analysis revealed a high-grade malignancy, and immunohistochemical analysis demonstrated diffuse expression of Melan-A, HMB-45, S100, and SOX10, with negativity for GATA3, CK7, CK20, and p63, confirming metastatic bladder melanoma. Subsequently, the patient developed rapid systemic progression with multiple brain metastases and septic shock of urinary origin due to ESBL-positive Klebsiella pneumoniae. Palliative management with whole-brain radiotherapy was initiated. Bladder metastasis of melanoma is a rare but clinically relevant entity, capable of mimicking primary urothelial carcinoma and leading to erroneous diagnoses. In patients with high-risk cutaneous melanoma, any bladder lesion should be considered metastatic until proven otherwise. Immunohistochemistry is essential to establish the melanocytic origin and guide appropriate management. Its identification usually reflects disseminated disease and is associated with aggressive progression and limited survival.