Prognostic indicators in WHO 2003 low‐grade endometrial stromal sarcoma

Aims: Endometrial stromal sarcoma (ESS) has traditionally been divided into low and high grade, but the World Health Organization (WHO, 2003) has changed the definition. Since 2003, many studies have used the old criteria, and few have focused on WHO 2003‐defined ESS low grade (ESS‐LG). The aim of this study was to investigate prognosticators in ESS‐LG. Methods and results: We reviewed the WHO 2003 diagnostic criteria in 91 tumours (previously classified as ESS low and high grade). There were 68 cases of ESS‐LG and 23 of undifferentiated endometrial sarcoma (UES). In the ESS‐LG cases, the prognostic value of clinicopathological variables was studied. With a median follow‐up of 79 months (range: 20–474 months), the recurrence and death rates were 5/68 (7%) and 1/68 (1.5%) in the ESS‐LG cases. Ovarian preservation or no ovarian preservation (P < 0.0001, hazard ratio (HR) 10.4) and mitotic activity index (MAI) (0–3 versus >3, P = 0.005, HR 8.6) had independent prognostic value. Other frequently used MAI thresholds – age, tumour diameter, and vessel invasion – were not prognostic. Among patients without ovarian preservation (n = 61), none of 53 with MAI 0–3 suffered recurrence, contrasting with two of eight (25%) of those with MAI >3 (P = 0.003); one of these two recurrence patients died (P = 0.02). Among patients with ovarian preservation (n = 7), three (43%) suffered recurrence but none died, and MAI had no additional prognostic value. Conclusions: In ESS‐LG, ovarian preservation and MAI >3 are associated with increased risk of recurrence.