Low-grade Smooth Muscle Tumors of the Primary and the Secondary Mullerian System

Some patients with bland smooth muscle tumors in the uterus have synchronous or asynchronous smooth muscle tumors in the peritoneum and/or the retroperitoneum. It is usually assumed that the uterine tumor is the primary lesion, and the extrauterine neoplasm represents its metastasis. Thus, they are designated as low-grade leiomyosarcomas because they lack the diagnostic features of a conventional spindle cell leiomyosarcoma. Nineteen such cases were retrieved from the files of the Department of Pathology at The University of Texas M.D. Anderson Cancer Center, covering a period of 18 yr. Institutional Review Board approval was obtained before the initiation of this study. In addition, 31 cases of conventional uterine leiomyosarcomas of a high grade were reviewed for comparison. Clinicopathologic features such as patients' age, tumor location, histologic features, stage, treatment, and follow-up were recorded. Immunohistochemical stains for estrogen receptor (ER), progesterone receptor (PR), p53, Ki-67, and WT-1 were performed in the initially detected tumor and the subsequent neoplasm of all cases with available material in the low-grade group and selected cases in the high-grade group. Compared with high-grade leiomyosarcomas, the low-grade group cases were found at an early age (45 vs. 52.8 yr), had a longer median time of "recurrence" (42 mo for the low-grade group vs. 12 mo for high-grade leiomyosarcomas), longer median survival (165 mo for the low-grade group vs. 41 mo for the high-grade group), and a much better overall survival (84% vs. 13%). Three (16%) patients died of disease in the low-grade group versus 27 (87%) patients in the high-grade leiomyosarcoma group. We also found a difference in the location of the extrauterine tumors. Most cases of low-grade tumors were found in the pelvis, abdomen, or retroperitoneum, whereas most high-grade leiomyosarcomas involved the lung. In the low-grade tumors, there were some differences in the immunophenotype between the uterine and the extrauterine neoplasms, but in the high-grade tumors, there were no differences in the immunohistochemistry between the primary tumor and the metastasis. In addition to these differences between the 2 groups in the age of the patients, sites of recurrences, and the immunophenotype of the uterine and extrauterine tumor, neither the uterine nor the extrauterine low-grade lesions had histologic features of malignancy. On the basis of these differences, the possibility that the extrauterine lesions in the low-grade group represent independent primaries involving the secondary mullerian system is proposed.