THE NEED FOR EPIDEMIOLOGIC STUDIES OF IN-SITU CARCINOMA OF THE BREAST

The purpose of this paper is to present background information on carc inoma in situ (CIS) of the breast and to provide a theoretical framewo rk for planning epidemiologic studies which may further our understand ing of breast cancer. Two types of epidemiologic studies are needed wh ich incorporate CIS of the breast: (i) case-control studies, in which in-situ lesions serve as disease outcomes (endpoints), and (ii) cohort studies and clinical trials, in which diagnosis of in-situ carcinoma serves as a starting point for patient treatment and follow-up. Case-c ontrol studies focusing on the causes of CIS have distinct advantages: if risk factors for cancer contribute to pathways involving some inte rmediate stages but not others (e.g. comedo-type but not non-comedo-ty pe DCIS; LCIS versus DCIS), the use of precursor lesions may more clea rly reveal risk factor associations than studies of invasive breast ca ncer alone; epidemiologic studies of precursor lesions are conducted c loser in time to the exposures suspected to be causes and may reduce r ecall bias or other forms of misclassification; genetic alterations in early lesions are more likely to represent causal events in developme nt of the malignant phenotype. Population-based case-control studies o f CIS may thus prove useful in understanding breast cancer etiology an d designing preventive strategies. CIS patients identified for case-co ntrol studies may be followed up over time as a cohort. Cohort studies (and clinical trials) of CIS aim to elucidate mechanisms influencing progression of CIS to invasive cancer as well as to evaluate effective ness of specific treatment modalities. Although the majority of CIS le sions of the breast are ductal carcinoma in situ (DCIS), epidemiologic studies which also include patients with lobular carcinoma in situ (L CIS) address potential differences between DCIS and LCIS with respect to both etiology and progression.