Abstract PD3-08: Effects of low dose tamoxifen on circulating risk biomarkers in a phase III trial in breast pre-invasive disease

Background: We recently showed that low dose (5mg/d) tamoxifen (babytam) for 3 years can halve the incidence of new breast neoplastic events in hormone sensitive or unknown breast pre-invasive neoplasia after surgery with limited toxicity (DeCensi et al JCO 2019; 37:1629-37). Here we report the results of circulating surrogate endpoint biomarkers of breast cancer risk with special attention to the risk of ovarian stimulation observed with the full dose in premenopausal women. Methods: Five hundred women 75 years old or younger were randomized to babytam or placebo (PLA). A subgroup of 406 women consented for collection of morning fasting serum at baseline (0), 1 (1Y) and 3 years (3Y) of treatment. There was a loss of about 25% of blood sampling at 3Y. Serum IGF-I, IGFBP-3, SHBG and C-reactive Protein (CRP) were performed on all available samples. Estradiol and testosterone were determined in a subsample (n=285) to determine the extent of ovarian stimulation by babytam in premenopausal women. We used Mann-Whitney test for univariate comparisons and linear regression modeling for multivariate analyses setting changes from baseline (1Y or 3Y minus baseline values) as dependent variable and treatment arm, age, BMI and baseline biomarkers values as explanatory factors. We tested treatment*menopausal status as interaction term. COX P-H model was used to calculate hazard ratio for CRP increase. Results: At baseline, all biomarkers were evenly balanced between arms (data not shown). IGF-I decreased significantly on babytam as compared to PLA. The difference of the changes between arms was -20 ng/mL after 1Y (p Citation Format: Harriet Johansson, Matteo Puntoni, Debora Macis, Valentina Aristarco, Aliana Guerrieri-Gonzaga, Davide Serrano, Silvia Caviglia, Laura Cortesi, Cristiana Taverniti, Antonio Ponti, Maria Grazia Pacquola, Marcella Gulisano, Fabio Falcini, Maria Digennaro, Anna Carriello, Katia Cagossi, Graziella Pinotti, Tania Buttiron Webber, Matteo Lazzeroni, Bernardo Bonanni, Luca Boni, Andrea DeCensi. Effects of low dose tamoxifen on circulating risk biomarkers in a phase III trial in breast pre-invasive disease [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr PD3-08.