Overexpression of the c-myc proto-oncogene occurs frequently in uterine sarcomas.

Overexpression of the c-myc proto-oncogene occurs in carcinoma of the ovary, endometrium, and cervix, and is associated with an adverse prognosis, but little is known about the pattern of c-myc expression in uterine sarcomas. This study investigates the expression of c-myc in uterine smooth muscle tumors and malignant mixed müllerian tumors. Twenty-three leiomyosarcomas, 10 leiomyomas, and 9 malignant mixed müllerian tumors were examined for c-myc overexpression by immunohistochemistry. Differences in mitotic rate and in survival were compared in c-myc positive and negative cases of leiomyosarcoma. Overexpression of c-myc was seen in 6/12 leiomyomas, 11/23 leiomyosarcomas, and 9/9 malignant mixed müllerian tumors. Positive staining was restricted to a perinuclear location in all of the leiomyomas and one leiomyosarcoma. Diffuse cytoplasmic staining was seen in the remaining 10 positive leiomyosarcomas. Positive staining was seen in both epithelial and stromal elements of malignant mixed müllerian tumors, including homologous and heterologous areas of stromal differentiation. There was no significant difference in mitotic rate or in survival between c-myc positive and negative cases of leiomyosarcoma. Overexpression of c-myc occurs in many uterine leiomyosarcomas and the majority of malignant mixed müllerian tumors. Overexpression of c-myc also occurs in benign uterine smooth muscle tumors but with a different pattern than that seen in malignant tumors. This overexpression does not correlate with survival and the significance of overexpression of c-myc in these tumors is unclear.