Gupta M, et al. - The frequency of an adverse outcome in smooth muscle tumors of uncertain malignant potential (STUMP) based on enhanced criteria was determined and a failure analysis for determining the feature(s) that aided in predicting the outcome was performed. A higher frequency of adverse outcomes compared to previous reports was shown, which indicated that more stringent criteria could exclude some from further follow-up. The frequent association with adverse outcome exhibited pathobiologic implications, despite significant nuclear atypia not being discriminatory. No particular correlation was determined between the presence of necrosis with adverse outcomes. It was noted that the adverse outcomes were heralded by atypical mitoses, epithelioid differentiation, vascular involvement, and infiltrative/irregular margins, and hence required inclusion into the diagnostic regimen.