Relationship Between Anthropometric Factors and Risk of Second Breast Cancer Among Women With a History of Ductal Carcinoma In Situ

BACKGROUND: Women with ductal carcinoma in situ (DCIS) have an elevated risk of a second breast cancer, but few data are available regarding the impact of modifiable lifestyle factors on this risk. METHODS: In a population-based case–control patient study of women with a history of DCIS in western Washington diagnosed between 1996 and 2013, 497 patients diagnosed with DCIS and a second ipsilateral or contralateral invasive or in situ breast cancer were enrolled. There were 965 matched control patients with one DCIS diagnosis. Associations between anthropometric factors and risk of an invasive or in situ second breast cancer event were evaluated using conditional logistic regression. Statistical tests were two-sided. RESULTS: Obesity (body mass index [BMI] ≥ 30 kg/m(2)) at initial DCIS diagnosis was associated with a 1.6-fold (95% confidence interval [CI] = 1.2 to 2.2) increased risk of any second breast cancer and a 2.2-fold increased risk of a contralateral second breast cancer (95% CI = 1.4 to 3.3) compared with normal weight women (BMI < 25 kg/m(2)). BMI and weight, both at initial DCIS diagnosis and at the time of the second breast cancer diagnosis, were positively associated with risk of any second and second invasive breast cancers (odds ratio = 1.01–1.04, all P ≤ .03). CONCLUSIONS: Although additional confirmatory studies are needed, obesity appears to be an important contributor to the risk of second breast cancers within the growing population of women with DCIS. This has potential clinical relevance with respect to identifying which women with a history of DCIS may require more careful monitoring and who may benefit from lifestyle modifications.