Spontaneous malignant mixed müllerian tumors and rhabdomyosarcoma of the uterus in rats.

Five malignant mixed müllerian tumors and one rhabdomyosarcoma were observed in LEWIS rats. Heterologous müllerian neoplasms (cases 1-4) consisted of epithelial and mesenchymal elements including squamous epithelium, glandular epithelium and sarcomatous, rhabdomyosarcomatous, cartilaginous as well as osseous parts. All the heterologous tumors revealed undifferentiated areas with an anaplastic appearance. The homologous müllerian tumor (case 5) was composed of glandular epithelium embedded in sarcomatous tissue. The rhabdomyosarcoma (case 6) consisted of bundles of elongated strap-like cells mixed with cells resembling rhabdomyoblasts.