Primary cardiac rhabdomyosarcoma: definition of a rare entity.

Primary cardiac rhabdomyosarcoma (PCR) is a highly malignant tumor that is rarely recognized prior to surgery or necropsy. We present the pathologic findings of a primary atrial rhabdomyosarcoma in an 82-year-old woman and an update on PCR as a clinicopathologic entity. In addition to pleomorphic tumor cells with cross-striations and a positive immunoperoxidase reaction for myoglobin, some areas of our patient's tumor had features of sarcoma botryoides. Electron optic studies showed primitive cells with fibroblastic and/or myoblastic differentiation. A comprehensive study of 77 cases in the international literature yielded new information and perspectives on PCR. The incidence of PCR is bimodal among males, being highest in infancy and early childhood with a secondary peak in the sixth and seventh decades. Females, however, have a single peak incidence in the fifth decade. Septal origin is 35.2% among infants and children but only 5.2% among adults. The predilection for the pediatric age group in conjunction with common septal origin among these patients suggests a congenital form of PCR that may arise from embryonic cell tests.