A case report published in Cureus describes metastatic melanoma identified four years after complete excision of a lesion originally diagnosed as melanoma in situ. The metastases involved the right ureter, porta hepatis, and thoracic spine and were confirmed through histopathology, immunohistochemistry, and urine cytology.
Melanoma in situ (MIS) is defined as melanoma confined to the epidermis and is generally considered noninvasive, with a low risk of metastasis after complete removal. In this case, a 77-year-old woman presented with hematuria, abdominal pain, fatigue, and nausea several years after excision of a biopsy-confirmed MIS. Imaging revealed an 11.3 cm lobulated porta hepatis mass, right-sided hydronephrosis caused by a 3.7 cm mid-ureteric lesion, and fluorodeoxyglucose-avid lesions in the porta hepatis, ureter, and T9 vertebra on positron emission tomography–computed tomography.
Because of the atypical locations, the initial differential diagnosis included primary urothelial carcinoma and other malignancies. Endoscopic ultrasound–guided biopsy of the porta hepatis mass confirmed metastatic melanoma based on morphology and immunohistochemical staining. Ureteric biopsy showed atypical epithelioid cells with focal necrosis and rare intracytoplasmic melanin pigment. Tumor cells were positive for S-100, Melan-A, and HMB-45 and negative for CK7, CK20, and GATA3, supporting metastatic melanoma rather than urothelial carcinoma.
Urine cytology demonstrated highly atypical cells with prominent nucleoli and high nuclear-to-cytoplasmic ratios, morphologically similar to the ureteric biopsy. Cystoscopy did not reveal a bladder mass. Histologic examination of tumor debris obtained during ureteroscopy confirmed melanoma with an identical immunophenotype to the porta hepatis lesion.
Dermatologic evaluation found no new primary cutaneous melanoma or local recurrence. The authors note that some lesions diagnosed as MIS may contain occult microinvasion detectable only with deeper sectioning or additional immunohistochemical studies, which could explain late metastasis in rare cases.
Metastasis of melanoma to the genitourinary tract is uncommon, occurring in approximately 0.2% to 1% of cases, and ureteral involvement is particularly rare. Clinically and histologically, such lesions may mimic primary urothelial carcinoma, highlighting the importance of comprehensive morphologic assessment and appropriate immunohistochemical panels in evaluating atypical ureteral tumors.
The patient was diagnosed with disseminated metastatic melanoma and referred for systemic immunotherapy with pembrolizumab.
This case underscores the need to include metastatic melanoma in the differential diagnosis of unusual genitourinary lesions, even in patients with a prior history of melanoma in situ. Accurate diagnosis depends on integration of clinical history, imaging, morphology, and immunophenotyping.
Source: Cureus
