Ductal carcinoma in situ (DCIS) is a precursor of invasive breast cancer; however, the majority of DCIS tumors do not progress to invasive breast cancer. Elucidating shared and distinct risk factors for DCIS and invasive breast cancer may provide novel insights into the pathogenesis of breast cancer.

The Multiethnic Cohort Study was used to examine whether known risk factors for invasive breast cancer are associated with DCIS among a racially and ethnically diverse U.S. population of women.

African American (HR 1.49, 95% CI 1.24–1.78), Native Hawaiian (HR 1.50, 95% CI 1.19–1.88), and Japanese American (HR 1.66, 95% CI 1.43–1.94) women were found to have a significantly higher risk of DCIS compared to White women, with Latino women having a non-significant increased risk (HR 1.19, 95% CI 0.97–1.48). Of the risk factors we investigated, increased risk of DCIS was associated with family history of breast cancer (HR 1.55, 95% CI 1.34–1.79), Type 2 diabetes (HR 1.27, 95% CI 1.09–1.48), nulliparity (HR 1.36, 95% CI 1.15–1.62), older age (> 30 yrs) at first live birth (p-trend 0.001), and current use of estrogen hormone therapy with or without progesterone (HR 1.19, 95% CI 1.04–1.35; HR 1.18, 95% CI 1.02–1.38, respectively). Decreased risk of DCIS was associated with parity, with a p-trend = 0.0001 for increasing number of children, and non-U.S. birthplace (HR 0.78, 95% CI 0.66–0.93). Risk factor associations did not differ significantly across racial and ethnic groups, with the exception of smoking status (p-het = 0.05), where an increased risk was found only for Native Hawaiians.

The identification of both shared and distinct risk factors of DCIS and invasive breast cancer underscores the need for other methods for risk stratification to differentiate indolent DCIS tumors from aggressive precursor lesions.