Stanford parameters stratify the risk of recurrence in gynecologic smooth muscle tumors of uncertain malignant potential

Smooth muscle tumor of uncertain malignant potential (STUMP) is an ill-defined category of neoplasms, which represent a diagnostic challenge. We aimed to assess whether the Stanford parameters, that is, high mitotic index (≥10/10HPF), significant atypia (moderate-to-severe), and coagulative tumor cell necrosis (CTCN), even when focal or ambiguous, may be used to stratify the risk of recurrence in gynecological smooth muscle tumor of uncertain malignant potential (STUMP). Electronic databases were searched from their inception to October 2019. All studies assessing the Stanford parameters in gynecological STUMP series were included. STUMPs were subdivided according to the presence of the three Stanford parameters: high mitotic index, significant atypia, and CTCN. A Kaplan–Meier survival analysis was performed for recurrence-free survival; hazard ratio (HR) was calculated in each category. Fourteen studies with 219 STUMPs were included. In 15.5% of cases, none of the three Stanford parameters were present, with a recurrence risk of 5.9%; 2.7% of cases showed high mitotic index alone, with a recurrence risk of 0% (HR = not calculable); 43.8% of cases showed significant atypia alone, with a recurrence risk of 18.7% (HR = 3.3; p = 0.012); 26.5% of cases showed CTCN alone, with a recurrence risk of 17.2% (HR = 3.1; p = 0.029); and 11.4% of cases showed at least two Stanford parameters, with a recurrence risk of 32% (HR = 7.5; p = 0.003). Stanford parameters may stratify the risk of recurrence of STUMP. Significant atypia and CTCN, but not high mitotic index, may be stand-alone risk factors for recurrence in STUMP. The presence of at least two Stanford parameters, even if equivocal (e.g., uncertain or focal CTCN, focal significant atypia, mitotic index around 10/10HPF), might still be enough to support a diagnosis of leiomyosarcoma. Further studies are necessary in this field.