Uterine leiomyoblastoma (epithelioid leiomyoma) neoplasm of low-grade malignancy. A histopathologic study.

Uterine leiomyoblastomas are neoplasms of smooth muscle origin, which despite their benign histopathologic characteristics, have been shown to invade locally, metastasize, and recur, resulting in the patient's death. In an effort to define possible cellular changes that could explain the disparity between histopathologic features and biologic behavior, we have studied a series of three uterine leiomyoblastomas that, in routine sections, exhibited benign morphological characteristics. A detailed histopathologic study revealed, in all three cases, randomly distributed clusters of neoplastic cells with overt malignant features, such as cellular and nuclear atypia, abnormal mitoses, local infiltrating tendencies, and vascular invasion. These findings suggest that uterine leiomyoblastomas should be viewed as neoplasms of low-grade malignancy of a distinct clinicopathologic entity.