Metastatic Renal Cell Carcinoma to the Luminal Colon with Autoamputation Phenomenon.

Introduction: Renal cell carcinoma (RCC) arises from the tubular epithelial cells in the cortex. RCC can present with metastatic disease in 25-33% of cases and has the potential to metastasize to every distant organ, with no apparent time limit for metastatic activity. Metastatic RCC to the colon is an infrequent phenomenon, making a new primary colonic adenocarcinoma an important differential. Multiple hypotheses for the mechanism of these metastases exist, including multistep hematogenous dissemination or a diffuse peritoneal seeding from an intra-abdominal or retroperitoneal tumor with colonic microperforations. Additionally, colonic metastases may outgrow their blood supply, leading to spontaneous detachment and passage in stool, a phenomenon known as autoamputation. This phenomenon has been described mostly in adnexa, ovaries, and related tumors such as teratomas, but also in polypoid carcinoma in the colon and rectum. Case Presentation: A 62-year-old male with a past medical history of known metastatic RCC, presented to the emergency department with multiple episodes of hematochezia and passed a large tissue-like mass in his stool. Colonoscopy revealed an ulcerated, obstructing mass in the descending colon with an inconclusive biopsy. However, the pathology from the initial mass passed through the stool revealed a clear cell-type RCC classic histologic pattern. Conclusions: To the authors' knowledge, this is the first reported case of autoamputation phenomena in metastatic RCC to the gastrointestinal (GI) tract. It represents RCC's propensity to metastasize to distant sites and should be considered in the differential diagnosis of lower GI bleed.