Regression of a congenital mesoblastic nephroma

Histologically, the cellular variant of congenital mesoblastic nephroma (CMN) is very similar to another rare tumor of infancy, infantile fibrosarcoma (IFS). In addition to the histologic similarities, these tumor types share cytogenetic abnormalities including translocation t(12;15)(p13;q25). We describe herein the case of a child who did not have immediate surgical resection of a CMN and whose tumor was untreated for 8 months. During that time, the tumor demonstrated a significant degree of regression. The shared translocation with IFS, a tumor with well-documented potential for spontaneous regression, suggests that this genetic abnormality may have contributed to the favorable clinical course.