Predictors Of Adverse Outcome In Uterine Smooth Muscle Tumors Of Uncertain Malignant Potential (STUMP): A Clinico-pathological Analysis Of 22 Cases With A Proposal For The Inclusion Of Additional Histologic Parameters

Abstract

Aims

Current WHO classification defines smooth muscle tumors of uncertain malignant potential (STUMP) as neoplasms that cannot be diagnosed reliably as benign or malignant using generally accepted criteria. This has led to application of various criteria sets; consequently, consistent and reliable outcome data is lacking. The aims of this study were: 1) to compare the frequency of adverse outcome in STUMP based on enhanced criteria; and 2) to perform failure analysis to identify feature(s) helpful in predicting outcome.

Methods and Results

Cases of STUMP diagnosed between 1994 and 2009 were retrieved and follow-up data collected. Morphological parameters were scored and correlated with outcome. 22 subjects with a median follow-up of 74.5 months (range: 26-166) formed the study group. Age ranged from 31.9 to 51.8 years (median 45.3). 16 subjects underwent hysterectomy and 6 had myomectomy. Adverse outcome was noted in 8 (36.4%) cases. Of cases with adverse outcome, notable features included moderate-severe nuclear atypia (7), epithelioid features (1), infiltrative or irregular margins (5), atypical mitoses (2), and vascular intrusion (3).

Conclusions

The frequency of adverse outcome in our series (36.4%) was higher than that of previously published reports (7-16%), suggesting that more stringent criteria can exclude some from further follow-up. Although "significant" nuclear atypia was not discriminatory, its frequent association with adverse outcome has pathobiological implications. Presence of necrosis was not particularly associated with adverse outcome. Atypical mitoses, epithelioid differentiation, vascular involvement and infiltrative/irregular margins appear to herald adverse outcomes, and therefore merit inclusion into the diagnostic regimen.

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