Rationale: Women with breast IEN have an annual risk of invasive disease equal to 8-10 times the general population, thus representing an important target for chemoprevention.

In the NSABP-P1 trial, tamoxifen use at 20 mg/day was associated with an 86% reduction of invasive breast cancer in women with previous ADH (RR=0.14, 95% IC, 0.03-0.47) and with a 56% risk reduction in women with previous LCIS (RR=0.44, 0.16-1.06). However, the increased risk of endometrial cancer and of venous thromboembolism, have significantly limited its broad use in chemoprevention.

To improve the risk-benefit ratio, the use of lower doses of the drug has been proposed. Recent trials from our group have shown that a dose of 5 mg/day does not increase endometrial proliferation and is associated with a decrease of the estrogenic activity of tamoxifen on IGF-I, SHBG and antithrombin-III, with a potential decrease of venous thromboembolic events. Moreover, tamoxifen exhibits a high tissue distribution, so that a dose of 5 mg/day attains at the breast tissue level a concentration 10 times higher than that needed to inhibit cell growth in vitro.

The CYP2D6 enzyme mediates oxidation of N-desmethyl tamoxifen to endoxifen, the most active metabolite of tamoxifen. The SNP CYP2D6*4 (1846G>A) allele accounts for 75% of CYP2D6 poor metabolizer phenotype which have been associated with a higher risk to develop a breast event compared to wildtype (Serrano D et al. Pharmacogenomics J. 2010 Mar 23).

Study design and enrollment report: This is a multicenter randomized double-blind placebo-controlled phase III trial with two parallel arms: tamoxifen at daily dose of 5 mg or placebo for a total treatment time of 3 years, to assess the efficacy and the safety of 5 mg/day tamoxifen to reduce breast cancer incidence in women with previous IEN (LIN 2-3 and ER-positive or unknown DIN 1b-3). At present no standard treatment exists to treat these women, particularly in Europe, where tamoxifen is not registered in women with prior DCIS (DIN 2-3). A total of 1400 women will be recruited in 3 years to detect a 50% reduction (Hazard Ratio = 0.5) in the incidence of breast cancer in the tamoxifen arm with an 80% power and a 1-sided 5% alpha level. Secondary endpoints include: incidence of other non-invasive breast disorders (i.e., LIN, ductal atypical hyperplasia), endometrial cancer, clinical bone fractures, cardiovascular events, venous thromboembolic events, and clinically manifest cataract. The pharmacogenetic endpoints include to assess whether CYP2D6 genotype can explain modulation on surrogate biomarkers of tamoxifen efficacy and safety, including circulating IGF-I, hormones, mammographic density, endometrial thickness and hot flashes, but also on clinical events.

As of July 27, 2010, 10 enrolment centers have been activated, n=128 women have been screened and n=44 have been randomized. 58 women refused to participate and 26 women were excluded for the following ineligibility reasons: 6 women for use of raloxifene, tamoxifen or other SERMs; 4 women for ER negative primary breast cancer; 3 women for bilateral mastectomy, 2 for previous thromboembolic events, 2 for age limits and 9 for other reasons. No serious adverse events or suspected unexpected serious adverse reactions were registered.

Citation Information: Cancer Prev Res 2010;3(12 Suppl):A70.

Copyright © 2010, American Association for Cancer Research
2010