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A well circumscribed uterine endometrial stromal tumor with smooth muscle differentiation recurred as a low grade endometrial stromal sarcoma: Is tumor margin enough for the diagnosis?

To the Editor: Differential diagnosis between the endometrial stromal nodule and the endometrial stromal sarcoma (ESS) is important for the management of patients; however, histological findings of the two lesions except the margins are not quite distinctive. Currently, diagnosis of endometrial stromal tumor with smooth muscle differentiation usually follows the diagnostic criteria of endometrial stromal tumors, and the myoinfiltrative tumor margin by thorough examination is only important to diagnose ESS. However, when a smooth muscle differentiation occurs at the periphery of ESS, the tumor forms a well defined border, thus, applicability of margin status as the diagnostic criteria becomes ambiguous. We describe this case to discuss the significance of margin status in the diagnosis of endometrial stromal sarcoma with smooth muscle differentiation. A 36-year-old, 2-0-2-2, woman had received a laparoscopy-assisted vaginal hysterectomy for two intramural masses. Six years after hysterectomy, a solid mass at the vaginal stump was detected on pelvic magnetic resonance image (MRI). Excision of vaginal stump mass with pelvic lymph node dissection was performed. No further recurrence is observed during 33 months after surgery. Initially, there were two well circumscribed uterine masses, measuring 9 cm and 5 cm in diameter, respectively. The larger mass in the fundus was well demarcated and easily shelled out from the surrounding myometrium. It had a bulging and lobulated cut surface with soft to rubbery consistency and homogeneously bright yellow to brown color. The smaller mass in the posterior wall were typical for leiomyoma. Microscopically, the periphery of the larger mass was well circumscribed (Fig. 1a) and composed of benign appearing smooth muscle bundles identical to those of typical leiomyoma. The central portion of the larger mass showed characteristic features of endometrial stromal tumor occupying approximately 60% of entire tumor volume and it was merged into the leiomyoma-like area, creating an irregular border between the two areas (Fig 1b). The tumor cells were composed of small, ovoid to spindle-shaped cells with scanty cytoplasm, and prominent spiral arteriole-like blood vessels (Fig. 1c). There were two to three mitoses per 10 high-power fields. Nuclear atypia or intravascular invasion was not identified in either area. In addition, a few microscopic nodules composed of endometrial stromal components were identified within the leiomyoma-like areas. The recurrent tumor at the vaginal stump showed homogeneously yellowish tan color and soft consistency without hemorrhage on gross examination. Microscopically, the tumor had characteristic histological features of low grade endometrial stromal sarcoma composed of endometrial-like stroma and blood vessels. The cellularity and the number of mitotic figures (5–6 /10 HPFs) were increased compared with the primary uterine tumor, and the foci of necroses were also identified. The tumor cells irregularly infiltrated into the subepithelial stroma and there were many intravascular tumor emboli. Smooth muscle differentiation was not identified in the recurrent mass. The immunohistochemical stainings were performed in the primary and recurrent tumors. The endometrial stromal tumor-like area in the primary uterine tumor showed strong immunopositivity for CD10 (Fig 2a), estrogen receptor (ER), progesterone receptor (PR), but negativities for desmin, calponin and smooth muscle actin (SMA) in contrast to the immunopositivity for demin, calponin (Fig. 2b) and SMA and negativities for CD10, ER and PR in the leiomyoma-like area at the periphery of primary tumor. Recurrent tumor cells had strong cytoplasmic expression for CD10, and strong nuclear expressions for ER and PR, but negativities for desmin and SMA. Myogenic differentiation in endometrial stromal tumor based on the immunohistochemical staining is not an uncommon finding. It can be seen in up to 30% of these tumors and does not warrant a separate diagnostic or prognostic entity. However, smooth muscle differentiation recognizable by routine light microscopic examination is relatively rare. An arbitrary cut-off point of 30% is currently used for designating ‘mixed’ endometrial stromal and smooth muscle tumors; however, the amount of either endometrial stromal or smooth muscle component does not seem to critically determine the clinical behavior of these mixed neoplasms, because recurrence and extensive invasion of the tumor have been observed in tumors composed predominantly of benign appearing smooth muscle components and a minor endometrial stromal tumor components. Among the recurrent tumors, some recurred as a low grade endometrial stromal sarcoma as in our case, and some as a mixed form. Thus, the histologically distinct stromal and smooth muscle components in the tumor seem to have transdifferentiation along the tumor recurrences or metastases. Pathology International 2012; 62: 363–365 doi:10.1111/j.1440-1827.2012.02801.x bs_bs_banner