gms | German Medical Science

Background: Breast cancer is the most common female cancer in the U.S. Approximately 20% of U.S. breast cancer patients are diagnosed with a non-invasive form of breast cancer called ductal carcinoma in situ (DCIS). DCIS is believed to be the earliest stage of invasive breast cancer; however, not all DCIS will progress to invasive breast cancer. We examined known risk factors for invasive breast cancer to determine whether they are also risk factors for DCIS among large numbers of minoritized racial and ethnic women.

Methods: We conducted a prospective analysis among 106,525 African American, Japanese American, Latino, Native Hawaiian, and White women in the Multiethnic Cohort (MEC) study conducted in Hawaii and California. After an average of 20.1 years of follow-up (1993-2019), 1,485 incident DCIS cases (81% in minoritized racial and ethnic groups) were identified by linkage to the statewide Surveillance, Epidemiology, and End Results cancer registries. Cox proportional hazards models were used to obtain hazard ratios (HRs) and 95% confidence intervals (CI) of primary DCIS and established invasive breast cancer risk factors obtained from baseline questionnaire. They included sociodemographic factors (race and ethnicity, birthplace, education, marital status), menstrual and reproductive factors (age at menarche, number of children, age at first birth, age and type of menopause, use of oral contraceptives and menopausal horrmone therapy (MHT), family history of breast cancer, diabetes, body mass index (BMI), BMI age 21, smoking, alcohol use, physical activity, and history of mammography.

Results: Compared to White women, a higher risk of DCIS was observed for African American (HR 1.48, 95% CI 1.23-1.78), Native Hawaiian (HR 1.56, 95% CI 1.24-1.96), and Japanese American (HR 1.69, 95% CI 1.45-1.98) women; no significant difference in risk was observed for Latino women. Overall, we observed an increased risk of DCIS associated with: family history of breast cancer (HR 1.57, 95% CI 1.35-1.83), being overweight (BMI 25-30 kg/m²; HR 1.14, 95% CI 1.00-1.30) or obese (BMI ≥ 30 kg/m²; HR 1.28, 95% CI 1.09-1.50) compared to normal weight (BMI 18.5-24.9 kg/m²), history of mammography screening (HR 1.88, 95% CI 1.47- 2.42), older age of first live birth (≥30 years; HR 1.29, 95% CI 1.01-1.64) compared to ≤20 yrs, and current use of MHT alone or with progesterone (HR 1.19, 95% CI 1.01-1.42; HR 1.23, 95% CI 1.06-1.43, respectively). A decreased risk of DCIS was observed for: younger age of natural menopause (<45 yrs; HR 0.74, 95% CI 0.57-0.96) compared to 50-59 yrs, having 2-3 and > 4 children (HR 0.83, 95% CI 0.70-0.99, HR 0.70, 95% CI: 0.57-0.85, respectively) compared to 1 child, some college education (HR 0.87, 95% CI: 0.76-0.99) compared to less than high school education, and non-U.S. place of birth (HR 0.80, 95 % CI 0.67-0.96). Risk of DCIS was not associated with physical activity, smoking, alcohol use, age at menarche, marital status, diabetes, and use of oral contraceptives.

Conclusions: These shared invasive breast cancer risk factors for DCIS, the earliest stage of breast cancer, may be suggestive of factors involved in breast cancer initiation.

The authors declare that they have no competing interests.

The authors declare that an ethics committee vote is not required.