Clinical outcome of atypical uterine smooth muscle tumors

15028 Background: Smooth muscle tumors of uncertain malignant potential (STUMP) and atypical leiomyomas have increased mitotic activity, cellular atypia and necrosis but the degree is less than that used to define uterine leiomyosarcomas. Our objective is to evaluate the clinical outcome of patients with uterine masses histologically defined as smooth muscle tumors of uncertain malignant potential or atypical leiomyomas. Methods: A thorough search of our institution’s pathology database from 1990 to 2005 was performed. A retrospective chart review was performed to obtain initial and subsequent treatments, documented recurrences and clinical outcomes. Pathology reports and slides were reviewed and the presence of atypia, necrosis and number of mitosis was recorded. Statistical analysis was performed by Student’s T-test. Results: Eighteen patients with a histologic diagnosis of atypical leiomyoma were identified with 14 STUMP, 2 bizarre leiomyomas, 1 myxoid and 1 mitotically active leiomyoma. The mean age of these patients was 41.8 years (range: 25–77) and was significantly younger than those with leiomyosarcoma (mean age was 54 years, p < 0.001). The histologic characteristics of the tumors included the presence of atypia at 50%, necrosis at 82% and mitoses at 94%. The rate of necrosis and number of mitosis was significantly less in the atypical group as compared to the leiomyosarcoma group (p values < 0.05). However the rate of cellular atypia was not statistically different between the two groups. The median follow-up period was 25 months, range 1–138 months. One of the eighteen patients developed a pelvic and pulmonary recurrence at which time a low grade leiomyosarcoma was diagnosed. The recurrence occurred 32 months after the initial diagnosis of a mitotically active leiomyoma. Sixteen patients demonstrated no recurrence or metastatic disease at the time of follow-up. Conclusions: Atypical leiomyomas appear to be diagnosed in younger women which leads to challenging treatment issues involving fertility preservation. While these tumors generally behave in a benign fashion, they have histologic characteristics that may allow for progression or recurrence. Close follow-up is warranted for patients who are diagnosed with atypical leiomyomas and smooth muscle tumors of uncertain malignant potential. No significant financial relationships to disclose.