Title: Biomarkers of Oxidative Stress as Predictors of Breast Cancer Risk in Women and Adolescent Girls
Description: Introduction: Despite intense research efforts and improvements to mortality rates, breast cancer remains the leading cause of premature cancer death for women. Identifying women at highest risk is vitally important for screening decisions that may have a critical impact on diagnosis and prognosis. A family history of breast cancer is a well-established risk factor, but it can be unreliable. An easily measured and accurate biomarker of breast cancer risk would be a significant advancement to public health by allowing targeted screening of women who would benefit most. It may also reveal underlying molecular mechanism that could illuminate pathways to prevention. Incidence rates of breast cancer have remained unmoved owing to the lack of known modifiable risk factors. This may be due in part because most breast cancer research has focused on behaviors and exposures in, or recalled from, adulthood. The studies detailed in this dissertation seek to investigate the associations between oxidative stress and breast cancer risk in both adult women and adolescent girls with a family history of breast cancer.

Methods: To determine the relationship between oxidative stress and breast cancer risk in adult women with a family history of breast cancer we measured and compared urinary levels of 8-OxodG and F2-Isoprostane in a prospective matched case control study nested within the New York Breast Cancer Family Registry. Cases (N=73) were individually matched with 2 controls on age, year of urine donation, menopausal status, and race. Conditional logistic regression methods were used to determine the odds of breast cancer from oxidative stress controlling for other risk factors for breast cancer and potential confounders. To better understand how oxidative stress levels change during puberty in girls and if such change is modified by a family history of breast cancer, we measured and compared levels of those same urinary biomarkers of oxidative stress in adolescent girls with and without a family history of breast cancer from the New York site of the Lessons in Epidemiology and Genetics of Adult Cancer from Youth cohort (LEGACY).

Oxidative stress levels were measured both cross-sectionally at baseline and longitudinally every 6-months for up to 18-months. Linear regression was used for the cross-sectional analysis and repeated measures analysis using mixed models was employed for the longitudinal analysis. In both studies, biomarker levels were measured using well-established ELISA methods and adjusted for hydration status using specific gravity. Results: In the case control study of adult women we found that both 8-OxodG and F2-Isoprostane levels were significantly associated with a reduced risk of breast cancer after adjusting for BRCA1/2 mutation status, time between menarche and parity or menopause, and BMI (8-OxodG: β10-unit= -0.14, OR=0.87, p=0.03; F2-Isoprostane: β10-unit = -0.53, OR=0.59 , p=0.03). This inverse association was strongest among women under 50 and in women with a BMI below 25 for both biomarkers, and among women who reached menarche before age 14 for F2-Isoprostane. Overall, women in the highest tertile of either oxidative stress biomarker had approximately 50% reduced odds of breast cancer diagnosis.

In our cross-sectional study of adolescent girls, we found that there was no significant difference in either oxidative stress biomarker in girls based on their family history of breast cancer. F2-Isoprostane levels were significantly associated with breast development measured by Tanner stage even after adjusting for age, age-specific BMI category and race (β=0.28, p=0.01). 8-OxodG levels were not significantly associated with age, BMI, race or Tanner stage at baseline but they were significantly associated with overweight/obese BMI but only among girls with a breast cancer family history (β=0.47, p=0.01). Change in 8-OxodG levels was significantly higher over the follow-up period in girls with a family history of breast cancer. This result remained significant after categorical measures of age, BMI, Tanner breast stage and race were added to the longitudinal model. F2-Isoprostane levels significantly increased in all girls over follow-up but this increase did not differ by family history of breast cancer, and the change was no longer significant our multivariate longitudinal analysis.

Discussion: In both adult women and adolescent girls we found significant associations between oxidative stress and breast cancer risk. In adult women, low levels of urinary biomarkers of oxidative stress may promote cancer progression. During adolescence, girls with a family history of breast cancer may be exposed to higher rates of DNA oxidation that could result in genetic mutations. The relationships between oxidative stress, breast development, family history, and BMI should be the focus of future investigations.