Peritoneal seeding following incomplete resection of mixed epithelial stromal tumor of the kidney: First case report.

Mixed epithelial stromal tumor (MEST) is rare and typically benign renal cystic neoplasm that cannot be clinically distinguished from cystic renal cell carcinoma. Its mainstay course of diagnosis and treatment remains surgical excision. Recurrence and malignant transformation is rare but has previously been described. To our best knowledge, we present the first case of peritoneal seeding resulting in a paracolonic MEST following incomplete resection in a patient with benign MEST. This signifies a new pathological behavior for MEST, predominantly, a benign kidney tumor. In addition, documentation with more cases of MEST is needed to further understand its pathogenesis, clinical behavior, malignant potential, and optimal management.