Cellular leiomyoma versus endometrial stromal tumor: A pathologists' dilemma.

Uterine smooth muscle tumors and endometrial stromal tumors (ESTs) are the two major types of mesenchymal tumors of the uterus, the latter being fairly uncommon. Among these, endometrial stromal sarcoma (ESS) accounts for 0.2-1.5% of all uterine malignancies. Although routine histopathological examination is sufficient to distinguish between ESS and smooth muscle tumors in most of the cases, the distinction between ESTs and highly cellular leiomyomas (CMs), on several occasions becomes a great diagnostic challenge for the pathologist. The differentiation between EST and CM is necessary on account of the variable clinical course and slight variation in the therapy. However, this is difficult due to the tendency of endometrial stromal cells to differentiate into well-developed smooth muscle cells as well as overlapping immunohistochemical profile in some cases. We hereby report a series of cases which posed a diagnostic challenge to us as to whether they are CMs or ESTs. We therefore discuss the histological features which helped us resolve this dilemma as well as the utility of immunohistochemistry (IHC) as a diagnostic aid in arriving at a final diagnosis in such problematic cases.