Abstract
BACKGROUND: Breast cancer treatment with selective estrogen receptor modulators (SERMs) increasesthe incidence of uterine malignant mixed Müllerian tumors (uMMMTs). We examine clinicopathologiccharacteristics and prognosis of SERM-associated uMMMTs (S-uMMMTs) and discusspossible pathogenetic mechanisms. METHODS: Among 28,104 patients with breast cancer, clinicopathologicfeatures and incidence of uMMMT were compared between patients who underwentSERM treatment and those who did not. Of 92 uMMMT cases that occurred during the same period,incidence, dose, and duration of SERM treatment, as well as overall survival rate, were comparedfor patients with breast cancer who underwent SERM treatment and those who did not (S-uMMMTvs NS-uMMMT) and for patients without breast cancer (de novo-uMMMT). Histopathologicalfindings and immunophenotypes for myogenin, desmin, p53, WT-1, estrogen receptor (ER) α, ERβ,progesterone receptor, and GATA-3 were compared between S-uMMMT and de novo-uMMMT. RESULTS: The incidence of S-uMMMT was significantly higher than that of NS-uMMMT (6.35-fold).All patients with SERM were postmenopausal and received daily 20-40 mg SERM. CumulativeSERM dose ranged from 21.9 to 73.0 g (mean, 46.0) over 39-192 months (mean, 107). Clinicopathologicfeatures, such as International Federation of Gynecology and Obstetrics stage andoverall survival, were not significantly different between patients with S-uMMMT and NS-uMMMTor between patients with S-uMMMT and de novo-uMMMT. All 11 S-uMMMT cases available forimmunostaining exhibited strong overexpression/null expression of p53 protein and significantlyincreased ERβ expression in carcinomatous and sarcomatous components. CONCLUSIONS: SERMtherapy seemingly increases risk of S-uMMMT development; however, clinicopathologic featureswere similar in all uMMMTs from different backgrounds. p53 mutation and increased ERβ expressionmight be involved in the etiology of S-uMMMT.