Fertility-sparing hormonal treatment in patients with stage I endometrial cancer of grade 2 without myometrial invasion and grade 1-2 with superficial myometrial invasion: Gynecologic Oncology Research Investigators coLLaborAtion study (GORILLA-2001).

Objectives: To evaluate oncologic and pregnancy outcomes of fertility-sparing treatment (FST) using progestin in patients with stage I grade 2 endometrioid endometrial cancer (EC) without myometrial invasion (MI) or grade 1-2 with superficial MI.

Methods: Multicenter data of patients with stage I grade 2 EC without MI or grade 1-2 EC with superficial MI, who received FST between 2005 and 2021, were analyzed. Cox regression analysis identified independent factors for progressive disease (PD) during the FST.

Results: Altogether, 54 patients received FST [medroxyprogesterone acetate (500-1000 mg) in 44, megestrol acetate (40-800 mg) in 10] with concurrent levonorgestrel-releasing intrauterine devices use in 31. With median time to achieve a complete response (CR) of 10 (3-24) months, 39 patients (72.2%) achieved CR. Of the 15 patients who attempted to conceive after achieving CR, 7 (46.7%) became pregnant (2 abortions, 5 live births). During a median FST duration of 6 (3-12) months, nine patients (16.6%) were diagnosed with PD. Fifteen (38.5%) experienced recurrence with a median recurrence-free survival of 23 (3-101) months. In the multivariable analysis, tumor size before FST ≥2 cm (HR 5.456, 95% CI 1.34 to 22.14; p = 0.018) was significantly associated with a high PD rate during FST.

Conclusion: The overall response rate to FST was promising, however, the PD rate was significant during the first 12 months of FST. Therefore, performing thorough endometrial biopsy and imaging studies is essential to strictly evaluate the extent of the disease every 3 months from FST initiation.