Predictors of adverse outcome in uterine smooth muscle tumours of uncertain malignant potential (STUMP): a clinicopathological analysis of 22 cases with a proposal for the inclusion of additional histological parameters

Aims: The current World Health Organisation classification defines smooth muscle tumours of uncertain malignant potential (STUMPs) as neoplasms that cannot be diagnosed reliably as benign or malignant according to generally accepted criteria. This has led to the application of various sets of criteria; consequently, consistent and reliable outcome data are lacking. The aims of this study were: (i) to compare the frequency of adverse outcome in STUMP on the basis of enhanced criteria; and (ii) 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 were collected. Morphological parameters were scored and correlated with outcome. Twenty-two subjects with a median follow-up of 74.5 months (range, 26-166 months) formed the study group. Their age ranged from 31.9 years to 51.8 years (median, 45.3 years). Sixteen subjects underwent hysterectomy and six underwent myomectomy. Adverse outcomes were noted in eight (36.4%) cases. In cases with adverse outcomes, notable features included moderate-severe nuclear atypia (seven), epithelioid features (one), infiltrative or irregular margins (five), atypical mitoses (two), and vascular intrusion (three) Conclusions: The frequency of adverse outcomes in our series (36.4%) was higher than that in previously published reports (7-26.7%), suggesting that the use of more stringent criteria can exclude some patients from further follow-up. Although -26.7% 'significant' nuclear atypia was not discriminatory, its frequent association with adverse outcomes has pathobiological implications. The presence of necrosis was not particularly associated with adverse outcomes. Atypical mitoses, epithelioid differentiation, vascular involvement and infiltrative/irregular margins appear to herald adverse outcomes, and therefore merit inclusion in the diagnostic regimen.