Purpose: To examine racial differences in smoking rates at the time of breast cancer diagnosis and subsequent survival among African American and non-African American women in the Carolina Breast Cancer Study (Phases I/II), a large population-based North Carolina study.
Methods: We interviewed 788 African American and 1,020 Caucasian/non-African American women diagnosed with invasive breast cancer from 1993 to 2000, to assess smoking history. After a median follow-up of 13.56 years, we identified 717 deaths using the National Death Index; 427 were breast cancer-related. We used Cox regression to examine associations between self-reported measures of smoking and breast cancer-specific survival within 5 years and up to 18 years after diagnosis conditional on 5-year survival. We examined race and estrogen receptor status as potential modifiers.
Results: Current (vs never) smoking was not associated with 5-year survival; however, risk of 13 year conditional breast cancer-specific mortality was elevated among women who were current smokers at diagnosis (HR 1.54, 95% CI 1.06-2.25), compared to never smokers. Although smoking rates were similar among African American (22.0%) and non-African American (22.1%) women, risk of breast cancer-specific mortality was elevated among African American (HR 1.69, 95% CI 1.00-2.85), but only weakly elevated among non-African American (HR 1.22, 95% CI 0.70-2.14) current (vs. never) smokers (P Interaction = 0.30). Risk of breast cancer-specific mortality was also elevated among current (vs never) smokers diagnosed with ER- (HR 2.58, 95% CI 1.35-4.93), but not ER+ (HR 1.11, 95% CI 0.69-1.78) tumors (P Interaction = 0.17).
Conclusions: Smoking may negatively impact long-term survival following breast cancer. Racial differences in long-term survival, as related to smoking, may be driven by ER status, rather than by differences in smoking patterns.
Keywords: Breast cancer; Mortality; Smoking; Survival analysis.