Cytogenetic findings in a case of congenital mesoblastic nephroma.

Congenital mesoblastic nephroma (CMN) is a benign, but locally aggressive, renal tumor of early infancy. Few metastases have been reported, but local recurrence is well documented. CMN is histologically distinct from Wilms' tumor and other childhood renal tumors, and is typically treated by surgical excision without adjuvant therapy. Cytogenetic abnormalities in these tumors have been described and are often compared with abnormalities seen in leiomyomas, fibromatoses, and infantile fibrosarcomas. In particular, trisomy 11 has been suggested as a nonrandom occurrence in CMNs. We describe a case of CMN in a 4-month-old female infant. The diagnostic histologic features included a monophasic mesenchymal appearance, prominent staghorn vascular spaces, and extensive infiltration of the adjacent kidney. Cytogenetic analysis showed a hyperdiploid chromosome number and a single structural abnormality involving a translocation between chromosomes 12 and 15. The composite karyotypic interpretation was: 46-47,XX,-X, +8, +11,t(12;15)(p12;q25), +17, +20[cp14]. The significance of karyotypic changes in this tumor is currently unknown. A genetic basis for histologic variability and progression may exist if certain cytogenetic abnormalities, such as trisomy 11 or specific translocations, confer a proliferative advantage. Additional cases are required to correlate cytogenetic findings with the biologic behaviors of CMN. We present this case as a contribution to existing literature describing these relatively rare and interesting renal tumors.