The Breast Cancer Continuum includes women at high risk, as in the Breast Cancer Prevention Trial; those with a history of atypical ductal hyperplasia (ADH) or lobular carcinoma in situ (LCIS); women with ductal carcinoma in situ (DCIS); those with <1 cm invasive disease or node-negative or node-positive disease; and those at risk of developing contralateral breast cancer. Women in all these categories benefit from therapeutic intervention with tamoxifen because each clinical state is associated with a certain probability of having early undiagnosed invasive breast cancer responsive to tamoxifen. This framework, relating these disorders to each other through their 5-year incidence of developing invasive breast cancer, leads to important conclusions relative to pharmaceutical drug development strategies, including chemoprevention investigations.