Congenital Disseminated Extrarenal Malignant Rhabdoid Tumor.

Soft tissue tumors arising in association with genetic or malformation syndromes have been increasingly reported. Malignant rhabdoid tumor (MRT) is a highly aggressive neoplasm of infancy and young childhood, characterized by typical morphology and biallelic inactivation of the SMARCB1 (INI1/hSNF5/BAF47) gene on chromosome 22q.2 which encodes a subunit of the SWI/SNF ATP-dependent chromatin remodeling complex. Congenital infantile disseminated MRT represents a unique clinicopathologic presentation of this tumor. We report a case occurring in a female neonate who presented at birth a voluminous left thigh mass. Surgical biopsy performed at day 9 showed morphology and immunoprofile of MRT. Staging evaluation identified hypercalcemia and distant nodules. The mass showed rapid growth. Despite chemotherapy, the tumor progressed with exteriorization through the biopsy scar. Chemotherapy was discontinued and treatment limited to palliative care and the child died on day 51. The tumor was homozygous for the SMARCB1 deletion with apparent de novo heterozygous germ line deletion in the infant, not identified in the parents.