Objectives: The aim of this study was to describe the clinicopathologic features and prognosis of endometrial cancer patients diagnosed during or after tamoxifen treatment for breast cancer.
Methods: Fifty-six tamoxifen-related endometrial cancers were identified from 10 hospitals in Japan. Past users were defined as endometrial cancer patients diagnosed more than 12 months after the cessation of tamoxifen treatment for breast cancer. All other users were classified as recent users.
Results: Age at diagnosis of the endometrial cancer ranged from 29 to 81 years. Sixteen (29%) and 19 (34%) patients were nulliparous and overweight, respectively. When the patients were divided into two groups: 30 recent and 26 past users, the distribution of various clinical characteristics, except for age at the time of diagnosis for endometrial cancer and the interval between the diagnoses of two cancers, was similar for two groups. The daily dose, duration and cumulative dose also showed no significant difference between the two groups. Past users had histopathologically more invasive tumors showing prognostically more unfavorable subtypes than recent users. The background lesions including endometrial polyps and diffuse cystic changes were similar for the two groups. The cumulative 3-year survival was significantly worse for past users than for recent users (74.8% and 96.4%, respectively, P < 0.04). In multivariate analysis including recentness of tamoxifen use and age at diagnosis of endometrial cancer, the significance of past user disappeared.
Conclusions: Past users had a worse prognosis of endometrial cancer with more invasive histologic features than recent users, probably because they included more elderly patients.