[1093] Predictors of Adverse Outcome in Smooth Muscle Tumors of Uncertain Malignant Potential (STUMP)

M Gupta, BJ Quade, MR Nucci. Brigham & Women's Hospital, Boston, MA

Background: Current WHO classification defines STUMP as tumors that cannot be diagnosed reliably as benign or malignant on the basis of generally accepted criteria. This has led to different criteria being used; therefore, reliable outcome data is lacking. The aim of our study was: 1) to compare the frequency of adverse outcome in STUMP based on our interpretation of published criteria; and 2) to perform failure analysis to identify feature(s) helpful in predicting outcome.
Design: Cases of STUMP between 1983-2008 were retrieved and follow up data collected. Morphological parameters (procedure type, age, lesion number and size, margins, cellularity, degree of cellular atypia, maximum mitosis/10HPF, and presence of necrosis or atypical mitoses) were scored and correlated with outcome.
Results: 20 subjects with a median follow up of 56 (range 12- 139) months formed the final study group. Age ranged from 31-60 yrs (median 47). 12 subjects underwent hysterectomy and 8 had myomectomy. The degree of nuclear atypia ranged from absent (2) to severe (6). Maximum mitotic count ranged from 0-8/10 HPF ; 4 cases had atypical mitoses. Necrosis was present in 7 lesions (1“geographic”, 2 ischemic, 4 indeterminate). Vascular intrusion was present in 1 case and 5 had infiltrative/ irregular borders. 15 (75%) subjects are alive with no evidence of disease (ANED). Adverse outcome was noted in 5 (25%) cases. Both cases with local recurrence (one as STUMP at 2 yrs and another as recurrent STUMP and then as LMS at 2.5 and 7 yrs, respectively) were treated with myomectomy and are ANED. 3 cases had metastasis and 2 were ANED at 5 and 3 years after metastasis, while the third died of disease. Of these cases with adverse outcome (n=5), notable features included moderate-severe nuclear atypia (5), focal epithelioid features (2), infiltrative/irregular margins (2), ≥5 mitoses/10HPF (1), atypical mitoses (1), and vascular intrusion (1).
Conclusions: The frequency of adverse outcome in our series was 25%, which is higher than previously published data (7-16%), suggesting that more stringent criteria can exclude some from further follow-up. Although “significant” nuclear atypia was not discriminatory in our series, its frequent association with adverse outcome has pathobiological implications. Ambiguous necrosis usually was associated with benign outcome, but was seen in the single fatal case. Atypical mitoses, epithelioid differentiation, vascular involvement and myometrial invasion appear to herald adverse outcomes, and therefore merit inclusion into the diagnostic regimen.
Category: Gynecologic & Obstetrics

Monday, March 22, 2010 8:00 AM

Platform Session: Section D, Monday Morning

 

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