Endometrial stromal sarcoma (ESS) is a rare disease with probably less than 700 new cases in the US or EU per year. ESS usually expresses steroidal receptors and is regarded to be hormone-sensitive. A higher risk in women receiving estrogen replacement therapy (ERT) or tamoxifen has been suspected, and remissions following treatment with progestins have been reported in case studies. Aromatase inhibitors represent an interesting new treatment option. Due to the rarity of the tumor, only few case series and no prospective studies are published. We therefore conducted a retrospective study to evaluate the influence of hormonal treatment to ESS.

Our institutional sarcoma data bank was screened for cases of ESS since 1999. All corresponding files and radiographs were reviewed retrospectively.

Ten patients with low-grade ESS were identified. Diagnosis was established before or by hysterectomy in 6 patients, by local recurrence after previous hysterectomy for nonmalignant disease in 3 patients or by pulmonary metastases with no primary tumor found so far in 1 patient. 5/10 patients were on ERT and 3/10 on tamoxifen at the time of diagnosis of metastatic disease. Treatment strategies consisted of stopping ERT and tamoxifen, respectively, or initiation of the progestin MPA or letrozole. Three patients achieved stable disease after stopping ERT. 2/3 patients responded to MPA as first-line treatment (1 CR; 50+ months, 1 PR; 9 months). 4/5 patients responded to letrozole as first-line therapy (3 PR;3+, 9+ and 10+ months) or second-line treatment after MPA (1 PR; 37+ months). 9/10 patients are alive 33 to 255 months after hysterectomy. Survival since diagnosis of metastatic disease is 4 to 164 months.

Patients with a previous history of low-grade ESS should not be treated with estrogens or tamoxifen. If nevertheless present, withdrawal of ERT or tamoxifen is strongly advised, resulting in disease stabilization in some cases. MPA and letrozole, in particular, are highly effective and lead to sustained disease control in most cases.