Early-Stage Predominance in Breast Cancer Diagnosis Among a Rural Population: Associations With Smoking Status in a 10-Year Registry-Based Cohort Study.

Background Rural populations face unique barriers to preventive care and cancer screening that may influence the timing and stage of breast cancer diagnosis. Although rural residence is frequently associated with delayed cancer presentation, population-based data characterizing diagnostic patterns in rural breast cancer patients, especially in the Upper Peninsula of Michigan, remain limited. This study aimed to explore the distribution of age and stage at breast cancer diagnosis in a predominantly rural population and to examine associations between smoking status, age at diagnosis, and stage of disease presentation. Methods We conducted a retrospective, population-based cohort study using the Upper Peninsula Health System (UPHS) tumor registry. The study consisted of women diagnosed with primary breast cancer between January 2013 and December 2023. Variables extracted included age at diagnosis, clinical stage, smoking status, and race. Descriptive statistics characterized demographic and clinical distributions. One-way analysis of variance (ANOVA) with Bonferroni-corrected pairwise comparisons assessed differences in age at diagnosis by smoking status. Chi-square testing evaluated the association between smoking status and stage at diagnosis (early vs. late). Results Among 1,061 staged cases, early-stage disease (stage 0, IA, IB) comprised 79.5% of diagnoses, with stage IA alone accounting for 45.3%. Age at diagnosis differed significantly by smoking status (F(3, 1193) = 19.83, p < .001): current smokers were diagnosed a mean of 4.6 years younger than never smokers (58.5 vs. 63.1 years, p < .001) and 8.4 years younger than prior smokers (58.5 vs. 66.9 years, p < .001). Stage at diagnosis also differed by smoking status (χ² = 8.47, p = .037), with current smokers having the highest proportion of late-stage disease (26.2%) compared with never smokers (21.0%) and prior smokers (15.5%). Younger (<40 years) and older (≥80 years) women had the highest rates of late-stage presentation. Conclusions In this predominantly rural referral population, breast cancer was diagnosed at early stages in nearly four of five cases. Current smoking was associated with both younger age at diagnosis and a higher proportion of late-stage disease, identifying tobacco use as a potentially modifiable factor influencing breast cancer detection patterns. These findings support continued investment in rural breast cancer screening infrastructure and advocate for integrating tobacco cessation into breast cancer prevention strategies.