Chromosome aberrations in uterine smooth muscle tumors: potential diagnostic relevance of cytogenetic instability.

Cytogenetic studies were carried out on a low-grade metastatic uterine leiomyosarcoma and on a large degenerating uterine leiomyoma. The leiomyosarcoma and leiomyoma were hyperdiploid and hypodiploid, respectively, and both tumors contained multiple consistent chromosome aberrations. In the patient with leiomyosarcoma, flow cytometric studies of proliferative foci from a previously resected uterine leiomyoma revealed near triploidy, suggesting that the leiomyosarcoma was metastatic from an unrecognized malignant uterine primary lesion. The leiomyosarcoma was characterized by extreme cytogenetic instability, whereas the leiomyoma demonstrated cytogenetic stability. The present cases and review of the literature on leiomyosarcomas and leiomyomas reveal cytogenetic instability to be very common in leiomyosarcomas (present in 8 of 10 cases) and uncommon in leiomyomas (present in 1 of 25 cases). A grading system is described which might be useful in evaluating the diagnostic and prognostic relevance of cytogenetic instability in uterine, and other, malignancies.