Abstract S6-1: Menopausal Hormone Therapy Influence on Cancer Incidence and Related Cancer Mortality in the Women's Health Initiative Randomized Trials

Abstract

Abstract The Women's Health Initiative (WHI) has conducted two phase III randomized placebo controlled trials evaluating menopausal hormone therapy. Conjugated equine estrogen 0.625 mg daily plus medroxyprogesterone acetate 2.5 mg daily (E+P) was evaluated in 16,608 postmenopausal women with no prior hysterectomy and conjugated equine estrogen alone 0.625 mg daily (E alone) was evaluated in 10,738 postmenopausal women with prior hysterectomy. Previous analyses suggested differences in E+P vs E alone influence on incidence and related mortality of several cancers. More recent analyses after additional follow-up clarify these issues and suggest a unifying hypothesis regarding hormone therapy influence on cancer. In cross study comparisons using multivariate Cox regression models statistically significant differences between the two WHI trials regarding E+P vs E alone influence on breast cancer incidence (P=0.01), colorectal cancer incidence (P=0.004) and deaths from non-small cell lung cancer (P=0.03) are seen. In addition, E+P, but not E alone, had a greater adverse influence on mortality attributed to breast cancer, colorectal cancer, and NSCLC then on the incidence of these cancers. Results are summarized below. Menopausal Hormone Therapy Influence on Incidence and Related Mortality of Selected Cancer Chlebowski JAMA 2003;289:3243, Chlebowski NEJM 2004;350:991, Stefanick JAMA 2006;242:1048, Ritenbaugh Cancer Epi Bio Prev 2008;17:2609, Prentice Cancer Epi Bio Prev 2009;18:1531, Chlebowski NEJM 2009;360:573, Chlebowski Gynecologic Oncology 2010;117:394; abst, Chlebowski Proc ASCO 2010;abst 1705 As estrogen plus progestin simulates angiogenesis, these findings suggest an hypothesis that, in addition to its influence on cancer incidence, combined E+P use, thru angiogenesis stimulation or other mechanisms, broadly enhances growth of already established cancers, differentially impacting cancer-related survival across several cancer categories. Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr S6-1.