Based on histological appearance, the accurate comparison of different variants of all described ESS cases is challenging because; (i) criteria for histological classification based on morphology varied in different studies and institutions, and/or they were not precisely specified, (ii) the number of cases in different categories was usually too small to make a precise conclusion on the frequency of JAZF1/SUZ12 fusion in ESSs of different histologic subtypes. The gene discussed is JAZF1; the disease is endometrioid stromal sarcoma.