Low-grade endometrial stromal sarcoma with extensive sex cord differentiation, heterologous elements, and complex atypical hyperplasia: Case report and review of literature

•Endometrial stromal sarcoma (ESS) may have sex cord differentiation, usually focal.•Diagnosis of ESS is difficult when variant morphology predominates.•Prognosis differs between ESS and UTROSCT; therefore, distinction is critical.•Extensive tumor sampling is mandatory to identify neoplastic endometrial stroma.•Sex cord differentiation may be associated with endometrial hyperplasia.