Cao H, et al. - In this retrospective study, researchers analyzed the clinical features, prognosis, and prevalence of unexpected uterine sarcoma (UUS) after hysterectomy and myomectomy for presumed leiomyoma. Records of women who experienced hysterectomy or myomectomy due to laparoscopy or laparotomy for preoperatively presumed uterine leiomyomas from January 2009 to December 2016 have been reviewed and data analyzed retrospectively. Twenty-six thousand six hundred forty-three patients had hysterectomy or myomectomy by laparoscopy or laparotomy for preoperatively presumed uterine leiomyomas in the hospital during the 8-year period. In the current study, only 0.33% of patients undergoing surgery for presumed leiomyoma experienced UUS. Endometrial stromal sarcomas (ESS) was the main UUS subtype, and the advanced stage seemed to have a negative impact on the ESS prognosis. However, it has not been shown that the time interval between initial therapy and secondary definitive surgery affects prognosis. Moreover, the small number of morcellation UUS patients (4 leiomyosarcomas and 7 ESS) may be underpowered to detect survival differences.