Figure 1.Influence of the cycle phase on breast total labeling index (TLI) of women less than 34 years of age according to whether cycles were natural or regulated by oral contraceptives (OC). (Reprinted with permission from Going JJ, Anderson TJ, Battersby et al. Proliferative and secretory activity in human breast during natural and artificial menstrual cycles. Am. J Pathol. 130:193-204, 1988