UTERINE SMOOTH-MUSCLE TUMORS OF UNCERTAIN MALIGNANT POTENTIAL

Objective: To determine whether tumors meeting the criteria of Hendric kson and Kempson for uterine smooth-muscle tumors of uncertain maligna nt potential have a natural history different from those of leiomyomas and leiomyosarcomas. Methods: Tumors with five to ten mitoses per ten high-power fields and with mild or moderate cellular atypia were clas sified as tumors of uncertain malignant potential. Tumors with two to four mitoses per ten high-power fields and severe cellular atypia woul d also be classified as tumors of uncertain malignant potential, but w e had no tumors that fell into this latter group. Forty-seven women wi th leiomyosarcoma or smooth-muscle tumors of uncertain malignant poten tial were identified. Paraffin-embedded blocks were recut, and hematox ylin and eosin-stained sections were studied for mitotic counts and ce llular atypia. Statistical analysis used x(2), Fisher exact test, Stud ent t test, and Kaplan-Meier life table analysis. Results: Fifteen tum ors were classified as uncertain malignant potential and 32 as leiomyo sarcomas. The patients with leiomyosarcoma were significantly older an d more likely to present with extrauterine disease. Those with tumors of uncertain malignant potential had a 5-year disease-free survival of 66% and overall survival of 92%, compared to 28 and 40%, respectively , for leiomyosarcomas; these differences were statistically significan t. Patients with tumors of uncertain malignant potential tended to hav e a protracted clinical course after development of recurrence, and se veral survived longer than 5 years with metastatic disease. Conclusion s: Patients with five to ten mitoses per ten high-power fields and mil d to moderate cellular atypia had a prognosis significantly better tha n that of patients with leiomyosarcomas. In this group, only 27% devel oped a recurrence, and after recurrence they tended to have a protract ed course. Some of these tumors do have a very aggressive course, and the term ''uncertain malignant potential'' is appropriate.