Background: Obesity is associated with advanced stage breast cancer at diagnosis and a poorer prognosis. Stage of breast cancer at diagnosis is also strongly influenced by the method of cancer detection. The objective of this study was to determine the relationship between body mass index (BMI) and breast cancer disease stage, taking into account the method of cancer detection (i.e., self-detection, screening mammography, and clinical breast examination [CBE]).
Methods: From 1988 to 1990, 2863 patients with invasive breast cancer were identified through a statewide, population-based, cancer reporting system and were interviewed as part of a larger study of breast cancer etiology. Stage of disease was classified as either localized or nonlocalized (regional and distant disease combined). The relation between BMI and disease stage was examined by using multiple logistic regression adjusting for age, education, race, year of diagnosis, and prior mammography use.
Results: Thirty-eight percent (1092 of 2863) of the women had nonlocalized breast cancer. A strong dose-response relationship was observed between increased BMI and the likelihood of nonlocalized disease (P < 0.001). However, this association was present only among the 55% of women (1585 of 2863) who self-detected their tumors. The odds ratios for nonlocalized cancer increased from 1.0 for the lowest quintile of BMI to 1.3, 1.6, 1.7, and 1.8 for the second through fifth quintiles, respectively, for this group.
Conclusions: Greater body mass was associated with nonlocalized breast cancer; however, this association was restricted to women who detected their own cancer. No association was found between BMI and stage of disease among cases detected by either mammography or CBE.