Breast tumor characteristics as predictors of mammographic detection: Comparison of interval- and screen-detected cancers

Background: Although mammographic screening is useful for detecting early b reast cancer, some tumors are detected in the interval between screening ex aminations. This study attempted to characterize fully the tumors detected in the two different manners. Methods: Our study utilized a case-control design and involved a cohort of women undergoing mammographic screening within the defined population of a health maintenance organization (the Group Health Cooperative of Puget Soun d). Women were classified as having "interval" or "interval-detected'' canc ers (n = 150) if their diagnosis was made within 24 months after a negative -screening mammogram or one that indicated a benign condition. Cancers were classified as "screen detected" (n = 279) if the diagnosis occurred after a positive assessment by screening mammography. Tumors from women in each g roup were evaluated for clinical presentation, histology, proliferative cha racteristics, and expression of hormone receptors, p53 tumor suppressor pro tein, and c-erbB-2 protein. Results: Interval-detected cancers occurred more in younger women and were of larger tumor size than screen-detected cancers. In unconditional logisti c regression models adjusted for age and tumor size, tumors with lobular (o dds ratio [OR] = 1.9; 95% confidence interval [CI] = 0.9-4.2) or mucinous ( OR = 5.5; 95% CI=1.5-19.4) histology, high proliferation (by either mitotic count [OR = 2.9; 95% CI = 1.5-5.7] or Ki-67 antigen expression [OR = 2.3; 95% CI = 1.3-4.1]), high histologic grade (OR = 2.1; 95% CI = 1.2-4.0), hig h nuclear grade (OR = 2.0; 95% Cf = 1.0-3.7), or negative estrogen receptor status (OR 1.8; 95% CI = 1.0-3.1) were more likely to surface in the inter val between screening examinations. Tumors with tubular histology (OR = 0.2 ; 95% CI = 0.0-0.8) or with a high percentage of in situ components (50%) ( OR = 0.5; 95% CI = 0.2-1.2) were associated with an increased likelihood of screen detection. Conclusions: Our data from a large group of women in a defined population i ndicate that screening mammography may miss tumors of lobular or mucinous h istology and some rapidly proliferating, high-grade tumors.