Introduction/Background The updated 2014 WHO Classification of Tumors of Female Reproductive Organs recognizes low and high grade endometrial stromal sarcoma (HGESS). HGESS is rare and it is unclear whether specific subtypes differ in prognosis.

Methodology HGESS patients treated from 2015 till 2022 were analysed for demographics, disease characteristics, treatment details and outcome.

Results HGESS was reported in 18 patients. Median age was 57(IQR 48–67); postmenopausal= 12; most common presenting symptom- vaginal bleeding= 15; mean tumor size in stage IA= 3.9cm(2.5–5), stage IB= 9.2cm(7–10.2), stage III-IV= 10cm(3.7–25). Hysterectomy with salpingo-oophorectomy: robotic= 3, laparoscopic= 1, open= 13 and no surgery= 1. Stage IA= 3, Stage IB= 7, Stage IIIC= 1, Stage IVA= 1, Stage IVB= 6. In addition to Cyclin D1 positivity, focal CD10 positivity was seen in 10 cases along with SMA(n=3),desmin(n=2) and caldesmon(n=1). Adjuvant therapy included observation (Stage IA=2, IB=4), radiotherapy and systemic therapy with ifosfamide plus adriamycin (Stage IA= 1, IB= 3). Systemic therapy was given in IIIC= 1, IVA= 1, IVB= 6 (Vemurafenib in 1, 2nd line Rucaparib in 1). Adjuvant therapy in Stage I High ESS was given before 2019, after which observation was adopted. Median OS of 20 months(95% CI 6–34). At last follow-up stage IA patients are disease free and alive, 3 out of 7 stage IB expired with relapse in lungs (pazopanib for 5 months), abdominal wall (palliative care for 1 month) and unknown site confirmed on telephonic follow-up. In Stage III & IV, 1 out of 8 patients is alive. 2-year PFS of Stage IA= 100%, Stage IB= 57.1%, Stage III & IV= 0%. Median follow-up for alive patients was 38 months(IQR 29–48).

Conclusion To our knowledge this is the largest series of HGESS reported from India. Stage IB and higher tumors have a poor prognosis and require newer therapeutic strategies to improve outcome.

Disclosures None.