Background: Many studies have investigated risk factors for developing breast cancer, but few have explored whether these risk factors are associated with the aggressiveness of the tumor. This case-case study examined the relationship between risk factors for breast cancer and the histological grade of the tumor at diagnosis, an important indicator of breast cancer aggressiveness.
Methods: We interviewed 215 breast cancer patients and obtained information on their demographics, reproductive history and hormone use. Grade of tumor was obtained from a review of the patients' pathological reports. The relationships between tumor aggressiveness (classified by tumor grade) and risk factors of interest were analyzed using multi-variable logistic regression. Maximum likelihood estimates of the odds ratio were obtained and 95% confidence intervals (CI) were calculated.
Results: In multivariable analyses we found that when comparing women who had their first child before age 20 with those who had their first child age 20 and older, women who had their first child before age 20 had approximately a 3.2 increased odds of having a higher-grade tumor (OR=3.20; 95% CI=1.20, 8.49). Long-term use of oral contraceptives, measured in years of oral contraceptive use, was also positively associated with a higher-grade tumor (OR=1.12; 95% CI=1.03-1.23). In addition we found that younger age at diagnosis was a strong predictor of a higher-grade tumor, with a 4% increased odds of having a higher-grade tumor for each year younger (OR=0.96; 95% CI=0.93-0.995).
Conclusions: Early age at first birth, long-term use of oral contraceptives, and younger age at diagnosis were associated with advanced tumor grade.