Effect Modifiers of Low-Dose Tamoxifen in a Randomized Trial in Breast Noninvasive Disease.

PURPOSE: Low-dose tamoxifen halved recurrence after surgery in a phase III trial in breast noninvasive disease without increasing adverse events. We explored the effect of low-dose tamoxifen in clinically relevant subgroups, including menopausal status, estradiol levels, smoking, body mass index, and proliferation of baseline lesion. PATIENTS AND METHODS: Incidence of invasive breast cancer or ductal carcinoma in situ was the primary endpoint. HRs and interaction terms were estimated using Cox models. RESULTS: A favorable HR and 95% confidence interval (CI) could be demonstrated for postmenopausal status (HR = 0.30; 95% CI, 0.11-0.82 vs. HR = 0.73; 95% CI, 0.30-1.76 in premenopausal women; P interaction = 0.13), women with estradiol less than 15.8 pg/mL, presence of menopausal symptoms at baseline, and never smoking (P interaction = 0.07), although the interaction P value was >0.05 for all characteristics. Efficacy was similar in all body mass index categories. Tumors with Ki-67 above the median level of 10% had a greater benefit (HR = 0.27; 95% CI, 0.09-0.81) than those with Ki-67 ≤10% (HR = 1.58; 95% CI, 0.45-5.60; P interaction = 0.04). CONCLUSIONS: The efficacy of low-dose tamoxifen seems to be greater in postmenopausal women and in women with lower estradiol levels. Benefits appear to be larger also in women with menopausal symptoms, never smokers, and tumors with Ki-67 >10%. Our results by menopausal status provide important insight into low-dose tamoxifen personalized treatment, although caution is necessary given their exploratory nature. Observation of an improved response in tumors with Ki-67 >10% is consistent but the use of the marker in this setting is investigational.See related commentary by Fabian, p. 3510.

Randomized Placebo Controlled Trial of Low-Dose Tamoxifen to Prevent Local and Contralateral Recurrence in Breast Intraepithelial Neoplasia.

PURPOSE: Tamoxifen administered for 5 years at 20 mg/d is effective in breast cancer treatment and prevention, but toxicity has limited its broad use. Biomarker trials showed that 5 mg/d is not inferior to 20 mg/d in decreasing breast cancer proliferation. We hypothesized that a lower dose given for a shorter period could be as effective in preventing recurrence from breast intraepithelial neoplasia but have a lower toxicity than the standard dose. PATIENTS AND METHODS: We conducted a multicenter randomized trial of tamoxifen, 5 mg/d or placebo administered for 3 years after surgery in women with hormone-sensitive or unknown breast intraepithelial neoplasia, including atypical ductal hyperplasia and lobular or ductal carcinoma in situ. The primary end point was the incidence of invasive breast cancer or ductal carcinoma in situ. RESULTS: Five hundred women 75 years of age or younger were included. After a median follow-up of 5.1 years (interquartile range, 3.9-6.3 years), there were 14 neoplastic events with tamoxifen and 28 with placebo (11.6 v 23.9 per 1,000 person-years; hazard ratio, 0.48; 95% CI, 0.26 to 0.92; P = .02), which resulted in a 5-year number needed to treat of 22 (95% CI, 20 to 27). Tamoxifen decreased contralateral breast events by 75% (three v 12 events; hazard ratio, 0.25; 95% CI, 0.07 to 0.88; P = .02). Patient-reported outcomes were not different between arms except for a slight increase in frequency of daily hot flashes with tamoxifen (P = .02). There were 12 serious adverse events with tamoxifen and 16 with placebo, including one deep vein thrombosis and one stage I endometrial cancer with tamoxifen and one pulmonary embolism with placebo. CONCLUSION: Tamoxifen at 5 mg/d for 3 years can halve the recurrence of breast intraepithelial neoplasia with a limited toxicity, which provides a new treatment option in these disorders.