[994] Uterine Smooth Muscle of Uncertain Malignant Potential: A Clincopathologic Analysis of 16 Cases from Multiple Centers

PPC Ip, ANY Cheung, PB Clement. University of Hong Kong, Queen Mary Hospital, Hong Kong, China; University of British Columbia, Vancouver General Hospital, Vancouver, BC, Canada

Background: The current WHO classification states that any uterine smooth muscle tumor that cannot be histologically diagnosed as unequivocally benign or malignant should be termed smooth muscle tumor of uncertain malignant potential (STUMP). STUMPs represent a heterogeneous group of rare tumors that have been the subject of only a few published studies, some of which lacked clinicopathologic details and/or follow-up data. More recently, it has been suggested that immunohistochemical staining may be helpful in the diagnosis of STUMPs.
Design: The clinicopathologic features of 16 cases of STUMP that exhibited usual smooth muscle differentiation and diagnosed between 1992 and 2006 from 11 hospitals were studied and classified into 4 subgroups using terminology and criteria described by Stanford investigators (Bell SW et al, Am J Surg Pathol 1994;18:535-558). Immunohistochemical stains for p16, p53, ki-67, and estrogen and progesterone receptors were performed. The results were compared with those in the literature.
Results: Six tumors wereatypical leiomyoma with limited experience (AL-LE), 7 of low malignant potential, NOS, 2 atypical leiomyoma, low risk of recurrence, and 1 mitotically active leiomyoma, limited experience. Follow-up was 21 to 192 months (mean, 80.5). Only 2 tumors recurred, at 15 and 51 months respectively; both were AL-LEs (multifocal moderate to severe atypia, no tumor cell necrosis, and mitotic counts of 4 & 5 mfs /10HPFs, respectively). Both tumors had areas that were indistinguishable from benign leiomyoma; both had diffuse immunoreactivity for p16 and p53. Six other tumors that had focal staining for these markers all had a benign outcome. Both patients with recurrence were alive at last follow-up (at 36 and 74 months). All the other patients were alive and disease-free.
Conclusions: These results and other recent reports indicate that the combination of p16 and p53 stains may be useful in predicting the behavior of STUMPs. These findings also support previous observations that the occasional STUMPs that recur often behave as a low-grade malignancy. Patients with a STUMP should receive long-term surveillance as the median time to recurrence may be as long as 5 years.
Category: Gynecologic

Wednesday, March 11, 2009 1:00 PM

Poster Session VI # 165, Wednesday Afternoon