Low-Grade Endometrial Stromal Sarcoma: Clinicopathologic and Prognostic Features in a Cohort of 102 Tumors.

Low-grade endometrial stromal sarcomas (LG-ESS) are the second most common malignant uterine mesenchymal tumors, but in contrast to the more common leiomyosarcomas, they are often characterized by a prolonged and relatively indolent course. However, a subset of patients experience significant morbidity or die of disease, and it is difficult to predict which tumors will behave aggressively, with most published studies limited in either the number of tumors or the depth of pathologic parameters evaluated. Thus, we studied the clinicopathologic features of LG-ESS in 102 patients ranging from 21 to 74 (median: 47) years. All were treated with hysterectomy and staged according to both the FIGO 2018 system (stage IA=22, IB=36, I-not otherwise specified=5, II=16, III=13, IV=10) and the FIGO 1988 system (stage I=62, II=1, III=17, IV=22). Tumors measured 1.2-49 (median: 7) cm. Microscopically, 69 involved the endometrium while 33 were centered in the myometrium. Thirteen showed only minimal infiltration of the myometrium while the rest displayed the typical extensive myometrial permeation. The cervical stroma was involved in 18, the uterine serosa in 27, and the parametrium in 22. Conventional morphology resembling proliferative endometrial stroma was seen in 95, fibroblastic appearance in 35, smooth muscle differentiation in 23, sex cord-like differentiation in 21, stromal hyalinization in 21, and myxoid stroma in 9. Less common features included glandular differentiation resembling adenomyosis (n=5), pseudopapillary pattern (n=1), deciduoid appearance (n=2), adipocytic differentiation (n=2), multinucleated cells (n=2), and rhabdomyoblastic differentiation (n=1). Mitoses ranged from <1 to 20 per 10 high-power fields (median=3). Lymphovascular invasion and infarct-type necrosis were present in 64 and 23, respectively. Follow-up was available in all patients ranging from 16 to 358 (median: 79) months. Forty-six received adjuvant treatment as hormonal therapy (n=34), radiation (n=4), radiation and hormonal therapy (n=4), chemotherapy (n=3), or chemotherapy and radiation (n=1). Three patients had persistent unresected tumor following surgery, and an additional 34 had recurrences at intervals of 3 to 272 (median: 79) months, including 2 tumors with minimal infiltration. At last follow-up, 75 patients were alive with no evidence of disease, 14 were alive with disease, and 9 died of disease at intervals of 16 to 167 (median=70) months. Four died of unrelated causes without recurrence. Five-year recurrence-free survival (RFS) and disease-specific survival (DSS) were 80% and 94%, while 10-year RFS and DSS were 51% and 87%, respectively. On statistical analysis, cervical stromal involvement ( P =0.018) and myxoid stroma ( P <0.001) were associated with shorter recurrence-free survival. Tumors lacking a conventional component had worse disease-specific survival ( P =0.048). All other clinical and morphologic features, including stage, were not significantly associated with outcome. On multivariate analysis, only cervical stromal involvement remained an independent predictor of recurrence-free survival ( P =0.047; HR: 16.939) and no factors were independently predictive of disease-specific survival. Our findings highlight the difficulty in predicting outcomes in these tumors, likely due to slow progression and frequent treatment responses even in the recurrent setting. We confirm the potential for recurrence even in tumors initially showing minimal infiltration. Cervical stromal involvement and lack of conventional morphology are potential novel risk factors that should be further evaluated in subsequent studies.