Objectives: To assess the nature of a series of unusual low-grade mucin-producing tubulocystic renal cancers diagnosed at the Mayo Clinic since 1985.
Methods: We reviewed the clinical, radiologic, and pathologic features of 13 unusual low-grade renal carcinomas with features most suggestive of collecting duct origin.
Results: In 8 cases, the tumor was discovered incidentally. Presenting symptoms in the other 5 patients were similar to those of typical renal carcinoma. Imaging studies and angiography disclosed solid, cystic, or complex masses that were relatively avascular. Pathologic assessment revealed good circumscription, minimal hemorrhage and/or necrosis, minimal tendency to extend beyond the kidney, tubulocystic architecture, a fibrotic interface with adjacent normal renal parenchyma, low nuclear grade, and minimal mitotic activity. Mucin production was noted in all evaluable cases. All tumors expressed keratins AE1/AE3 and/or Cam 5.2. The tumors showed immunoreactivity to antibodies directed against keratin 34 beta E12 (8 of 13 cases), and Ulex Europeus antigen 1 (6 of 10 cases). Follow-up ranged from 12 to 114 months (mean 62). No metastases occurred in 12 patients. One patient died of metastatic carcinoma morphologically identical to the primary renal neoplasm 46 months after his tumor had been misinterpreted as a benign condition.
Conclusions: We believe the tumors described in this article may be of collecting duct origin, representing the low-grade end of a spectrum of cancers arising in collecting duct epithelium.