S3729 Colonic Metastasis of Renal Collecting Duct Carcinoma: An Unusual Presentation

Introduction: Renal cell carcinoma (RCC) accounts for 3% of adult cancers with clear cell RCC (CCRCC) being its most prevalent subtype. Collecting duct renal cell carcinoma (CDRCC), is a rare variant that accounts for 1% of all RCC cases. CDRCC carries a poor prognosis. This malignancy originates from the distal medullary collecting duct. Metastasis of CCRCC to colon is uncommon. Colonic metastasis of the CDRCC variant has not been previously reported. We present the first case of CDRCC with metastasis to the colon detected during a routine screening colonoscopy. Case Description/Methods: A 48-year-old African American man presented for routine index colonoscopy. Past medical history was significant for marginal zone lymphoma in remission and metastatic (Stage T4 N1). CDRCC treated with left nephrectomy and chemotherapy. He was asymptomatic. Social and family history was unremarkable. Prior to colonoscopy, a computed tomography (CT) of the abdomen and pelvis showed no metastatic disease. The colonoscopy revealed a 5 cm descending colon mass causing partial luminal obstruction. Biopsy of colon mass showed CDRCC. Patient underwent left hemicolectomy. On 1 year follow up, the patient is asymptomatic, and imaging demonstrated no evidence of recurrent CDRCC. Discussion: Renal cell cancers typically present in the sixth and seventh decades of life, with male to female ratio of 2:1. Four percent of these tumors are familial. CDRCC is a rare variant of CCRCC. The CDRCC is more common in African Americans and presents with locally advanced (T3-4) disease, distant metastasis and nodal involvement. 3-year disease specific survival for CDRCC is 58%. CDRCC metastasizes to lymph nodes, lungs, pleura, bones and liver. Colon metastasis of CDRCC in our case, is a novel finding. Thin slice CT has higher sensitivity for detecting local recurrence and metastatic disease. CT scan findings of medullary location, weak and heterogeneous enhancement, infiltrative growth, preserved renal contour and cystic component may predict ductal cell histology. Histologically, CDRCC exhibits high grade tubular morphology and infiltrative growth accompanied by stromal desmoplasia. Surgery is the mainstay of the treatment. Treatment for metastatic disease is chemotherapy. Five years survival after nephrectomy is poor. The median survival is 16 months. This case underscores the rarity of metastatic CDRCC to the colon. Since no previous case of CDRCC with metastasis to colon has been documented, this finding may be prognostic.