RISK OF ENDOMETRIAL CANCER IN BREAST-CANCER PATIENTS UNDER LONG-TERM ADJUVANT TREATMENT WITH TAMOXIFEN

Aims: To evaluate the relative risk of endometrial cancer with respect to the expected underlying incidence in breast cancer patients underg oing long-term adjuvant tamoxifen therapy. Methods: A total of 1010 po stmenopausal breast cancer patients receiving adjuvant tamoxifen and w ith a first negative endometrial ultrasonography (cutoff for abnormal endometrial thickness >5 mm) were followed by annual transvaginal ultr asonography. Abnormal endometrial thickness prompted an outpatient end ometrial biopsy or curettage under anesthesia in the case of cervical stenosis and increasing endometrial thickness. The standardized incide nce ratio (SIR) with respect to underlying incidence was determined. R esults: A total of 1,010 eligible subjects who had been receiving tamo xifen for an average of 51 months were enrolled and followed for a tot al of 2,361 patient-years between January 1993 and Decem ber 1996. Fiv e cases of endometrial cancer were observed in the study period: 1 was detected at screening, and 4 were diagnosed for vaginal bleeding in t he interval between screen-examinations. SIR was 4.0 (95% confidence i nterval, 1.3-9.4) and increased to 4.8 (CI, 1.6-10.5) when the single cancer detected at first screening was considered as incident. Conclus ions: This study adds evidence to the hypothesis that longterm tamoxif en treatment may be responsible for a relevant increase in the risk of developing endometrial cancer. Surveillance based on endometrial ultr asonography was poorly sensitive, but the favorable stage at diagnosis of screen-detected or interval endometrial cancers does not support a more aggressive screening approach.