Santen RJ, Heitjan DF, Gompel A, et al. - Given breast cancer risk attributable to use of estrogen alone and estrogen plus a synthetic progestogen for < 5 to ≥ 15 years of use was calculated in the recent Collaborative Group on Hormonal Factors in Breast Cancer (CGHFBC) publication, researchers determined attributable risks from the data published by the CGHFBC, taking different degrees of underlying risk into account. Three classes of risk were defined on the basis of the Endocrine Society Guideline on Menopausal Hormone Therapy (MHT): low (1.5%), intermediate (3.0%), and high (6.0%) underlying risk of breast cancer over 5 years. An increment in attributable risks of MHT, from 12, to 42, to 85 additional women per 1000, was noted in the low, intermediate, and high-risk groups respectively, among women receiving estrogen plus a synthetic progestogen for 5–9 years. The observed attributable risks for estrogen alone were found to be lower but also increased depending on underlying risk. Findings revealed an amplification of the attributable risks with the duration of MHT use which resulted in an increase in both relative risk as well as breast cancer incidence.