Pooled associations of categorical mammographic density for tumor type and morphological subtypes of invasive breast cancer by age. Odds ratios and 95% confidence intervals adjusted for age, body mass index, and study are shown for each category of mammographic density (MD): 1, 0 to 10% MD; 2, 11 to 25% MD (reference); 3, 26 to 50% MD; 4, 51% + MD). (A) Tumor type. (B) Histology. (C) Tumor grade. (D) Tumor size. (E) Lymph node involvement. (F) Estrogen receptor (ER) status. (G) Progesterone receptor (PR) status. (H) Human epidermal growth factor receptor 2 (HER2) status. DCIS, ductal carcinoma in situ.