Heterogeneity in lobular composition is independent of age, breast quadrant, and presence of cancer. A. Individual lobular composition in a cohort of nulliparous women ≤45 years of age (n = 23 cases). Among women, there is marked variation in lobule type; type 1 (green), type 2 (yellow) and type 3 (pink) (n= >550 lobules). B. Lobular composition of breast in nulliparous women does not vary by age increments of five years (≤35 years versus ≤30 years (P = 0.89); ≤40 years versus ≤30 years (P = 0.62); ≤45 years versus ≤30 years (P = 0.19)) C. Lobular composition in an expanded cohort excluding recently pregnant and lactating women (n = 82 cases) similarly shows lobular composition is not age dependent (≤35 years versus ≤30 years (P = 0.35); ≤40 years versus ≤30 years (P = 0.18); ≤45 years versus ≤30 years (P = 0.34)) D. Breast quadrant analysis from three mastectomy cases demonstrated no differences in lobular types for all quadrants (LO versus LI (P = 0.33); UI versus LI (P = 0.40); UO versus LI (P = 0.25)). E. Lobular type composition does not vary between women who were subsequently diagnosed with cancer (n = 82 cases) or were cancer free (n = 7 cases) (P = 0.59), or (F) by the presence (n = 47 cases) or absence (n = 24 cases) of ER expression in the adjacent tumor (P = 0.15). G. Lobular type composition is not significantly influenced by hormonal effects of the menstrual cycle as depicted by initial and subsequent breast biopsies two to three weeks apart (n = 12 cases) for type 1 (P = 0.38), 2 (P = 0.32) and 3 (P = 0.46) lobules. All error bars represent standard error of the mean (SEM). LI, lower inner; LO, lower outer; UI, upper inner; UO, upper outer.