Comparison of risk factors for ductal carcinoma in situ and invasive breast cancer.

BACKGROUND: Ductal carcinoma in situ (DCIS) accounts for approximately 12% of newly diagnosed breast cancers. Knowledge of the factors that predict who will be diagnosed with DCIS is very limited.
PURPOSE: The goal of this study was to determine risk factors associated with DCIS and whether these risk factors are similar to those associated with invasive breast cancer.
METHODS: We conducted a cross-sectional study of 39,542 women aged 30 years and older who underwent a screening mammographic examination at the University of California San Francisco Mobile Mammography Screening Program from April 1985 through September 1995. A breast cancer risk profile and clinical history were obtained for each woman. Follow-up after abnormal mammography was performed to determine the presence of DCIS or invasive breast cancer by contacting the women's physicians and by linkage to the regional Surveillance, Epidemiology, and End Results cancer registry. Multivariate analysis was performed by the use of polytomous logistic regression. Two-sided statistical tests were used to determine P values.
RESULTS: Among women aged 30-49 years, a family history of breast cancer (i.e., at least one affected first degree relative) was associated with an increased risk of DCIS (Odds ratio [OR] = 2.4; 95% confidence interval [CI] = 1.1-4.9) and body mass index greater than or equal to 25 kg/m2 was associated with a decreased risk of DCIS (OR = 0.4, 95% CI = 0.2 to 0.9). For each of these factors, there was a trend in the same direction bordering on statistical significance for invasive cancer (ORs = 1.7 [95% CI = 0.9-3.4] and 0.6 [95% CI = 0.3-1.1], respectively). Report of a palpable mass was associated with an increased risk of invasive cancer among women aged 30-49 years (OR = 12.0; 95% CI = 7.1-20.0); there was a trend in the same direction for DCIS (OR = 2.0; 95% CI = 0.8-5.1), but the association was much stronger for invasive disease than for DCIS (OR = 6.0; 95% CI = 2.1-18.0; P = .001). Among women aged 50 years and older, family history of breast cancer and nulliparity or age at birth of first child of 30 years or older increased the risk of both DCIS (ORs = 2.2 [95% CI = 1.0-4.2] and 2.3 [95% CI = 1.3-3.8], respectively) and invasive breast cancer (ORs = 1.5 [95% CI = 1.0-2.2] and 1.6 [95% CI = 1.2-2.1], respectively). Report of a palpable mass was not associated with an increased risk of DCIS among women 50 years and older, but it was strongly associated with an increased risk of invasive cancer (OR = 9.3; 95% CI = 6.0-14.0). Increasing age was associated with an increased risk of both DCIS and invasive cancer among women aged 30-49 years, but the association was stronger for invasive disease; a trend in the same direction bordering on statistical significance was observed for women aged 50 years and older.
CONCLUSION: Risk factors for DCIS are similar to those for invasive breast cancer. IMPLICATIONS: More research is needed to better understand the malignant potential of DCIS lesions and factors that predict which lesions will become invasive breast cancer if left untreated.