Prominent decidualization following progestin treatment for endometrial hyperplasia and carcinoma as a mimic of large residual tumor: A cautionary tale

OBJECTIVE: Progestin-based therapy is common for patients with endometrial neoplasia who desire fertility preservation, but some patients ultimately require surgery. Intraoperative assessment, which can use gross lesion size, may impact the extent of surgery performed. We sought to characterize the extent to which grossly identified lesions in the setting of progestin therapy correspond to microscopic findings. METHODS: Thirteen hysterectomy specimens with progestin-treated atypical hyperplasia or endometrioid carcinoma were identified. Clinicopathologic factors were collected by chart review. Slides were assessed for the extent to which decidualized stroma (DS) comprised grossly identified lesions and comparisons were drawn with tumor size, age, and menopausal status. RESULTS: Mass lesions were described in 11 cases with a median of 4.5 cm (range 1–8.2) and the 2 cases without discrete masses had diffuse thickening. Two patients had only focal residual hyperplasia despite having mass lesions (7 & 2.2 cm). DS was more prominent in premenopausal patients (median 65%, range 10–90%) than in postmenopausal patients (median 18%, range 10–40%; p = 0.06). The distribution of DS throughout mass lesions was variable. CONCLUSIONS: Large mass lesions following progestin therapy may histologically consist of DS with little to no residual neoplastic disease, such that perceived tumor size does not necessarily reflect extensive residual disease, especially in pre-menopausal patients. Intraoperative gross assessment alone may lead to unnecessary lymphadenectomy and/or oophorectomy, but this can potentially be prevented by using frozen section.