The increasing trend in Japan of müllerian mixed tumor of endometrium

An increasing trend in Japan of Müllerian mixed tumor (MMT) of the endometrium has been suspected from both the Annual Pathological Autopsy Records in Japan (APARJ) and an analysis of surgical cases from the National Cancer Center Hospital (NCCH). One hundred and four MMT cases were recorded in APARJ during the period, 1965-1984, which constituted 1.1% of all malignant uterine tumors. The number of MMT cases in the past 10 years (87 cases during the period, 1975-1984) increased more than fivefold over that of the previous 10 years (17 cases during the period, 1965-1974). The proportion among malignant uterine tumors also increased from 0.5 to 1.5%. Eighteen patients with MMT underwent surgery in the NCCH during the period, 1963-1986, which accounted for 4.3% of endometrial malignant tumor cases. Of these only one was resected during the 12-year period, 1963-1974, while there were 17 surgically resected cases during the 12 years from 1975 to 1986. These represented 0.8 and 5.7%, respectively of malignant tumors of the endometrium during the two periods. In five out of 18 cases, MMT occurred as a second primary malignancy, and in all cases the histology was one of mesodermal mixed tumor. It was suggested that its occurrence as a second primary malignancy would be contributing to the recent increase of MMT in Japan.