An Uncommon Journey of Melanoma In Situ: A Case Report of Metastasis to the Ureter and Porta Hepatis With Positive Urine Cytology.

Melanoma in situ is typically associated with an excellent prognosis following complete excision, with metastatic spread considered exceedingly rare. We present an exceptionally rare case of a 77-year-old woman with a history of completely excised melanoma in situ diagnosed four years back, who developed obstructive uropathy. Imaging revealed masses involving the ureter, porta hepatis region, and spine. Histopathological analysis of samples obtained via endoscopic ultrasound (EUS)-guided porta hepatis biopsy and ureteral tumor debris collected during cystoscopy confirmed Melan-A and S-100-positive metastatic malignant melanoma. No evidence of a new or recurrent primary cutaneous lesion was identified. This case highlights the rare potential for late and distant metastasis from melanoma in situ, including to atypical sites such as the ureter. It emphasizes the necessity of maintaining careful clinical monitoring throughout long-term follow-up.