A Rare Case of Metastatic Urothelial Carcinoma and the Importance of Immunohistochemical Profiling

Summary: Although lung and kidney cancers are common sources of scalp metastases in men, metastatic cutaneous urothelial carcinoma is rare and typically indicates poor prognosis. Skin biopsy remains the gold standard for diagnosing cutaneous metastases, underscoring the crucial role of dermatopathologists. We present a 73-year-old male with history of high-grade urothelial carcinoma of the renal pelvis and bladder, treated with nephroureterectomy and Bacillus Calmette-Guérin, who presented with a 3-week history of a firm pink nodule on the frontal scalp and a thigh mass. A CT scan of head, chest, and thigh revealed a scalp mass with indistinct margins, an infrahilar lung mass and multiple nodules, and a left vastus lateralis mass with central necrosis, respectively. Skin biopsy of the scalp mass revealed a poorly differentiated dermal malignancy composed of epithelioid, pleomorphic cells. Immunohistochemical analysis showed positivity for p63, CK7, and PAX8, while Sox10, GATA3, uroplakin, napsin-A, TTF-1, LCA, and CK20 were negative. The diagnosis of metastatic urothelial carcinoma was confirmed. The patient is planned for treatment with pembrolizumab and enfortumab vedotin. This case emphasizes the need for maintaining a broad differential diagnosis in patients with a history of malignancy, with immunohistochemistry playing a crucial role in expediting accurate diagnoses and treatment.