Clinical implications of morular metaplasia in fertility-preserving treatment for atypical endometrial hyperplasia and early endometrial carcinoma patients

OBJECTIVE: Morular metaplasia (MM) is a benign epithelial metaplasia that sometimes appears in atypical endometrial hyperplasia (AEH) and endometrioid endometrial carcinoma (EEC). However, the clinical implications of MM for fertility-preserving treatment in AEH and EEC patients are unclear. This study investigated the clinical features and impact of MM on the efficacy of fertility-preserving treatment. METHODS: We retrospectively studied 427 AEH and EEC patients who received fertility-preserving treatment. Clinical features, treatment efficacy, and onco-fertility results were compared between patients with and without MM. RESULTS: MM appeared in 147 of 427 (34.4%) patients. Among them, 49 (33.3%) had MM only before treatment (BEF group), 32 (21.8%) had sustained MM before and during treatment (SUS group), and 66 (44.9%) had MM only during treatment (DUR group). The BEF group had a higher 12-month CR rate (98.0% vs 85.7%, p = 0.017) and shorter therapeutic duration to achieve CR (4.0 vs 5.7 months, p = 0.013) than the non-MM group had. In comparison with the non-MM group, the SUS and DUR groups had a lower CR rate after 7 months of treatment (SUS vs non-MM, 37.5% vs 61.1%, p = 0.010; DUR vs non-MM 33.3% vs. 61.1%, p < 0.001), and a longer median therapeutic duration to achieve CR (SUS vs non-MM, 7.6 vs. 4.0 months, p = 0.037; DUR vs non-MM, 7.9 vs. 4.0 months, p < 0.001). CONCLUSION: Appearance of MM only before treatment was positively correlated with outcome of fertility-preserving treatment, while sustained MM or appearance of MM only during treatment implied poorer outcome of fertility-preserving treatment in AEH and EEC patients. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s00404-021-06382-3.