Prevalence of BRCA1 and BRCA2 mutations in women with breast carcinoma In Situ and referred for genetic testing.

Ductal and lobular carcinoma in situ (CIS) accounted for 62,280 (24.5%) of all new breast cancer diagnoses in 2009. BRCA1/2 mutations confer an extremely high risk of breast cancer, and management guidelines for BRCA1/2 mutation carriers advise close follow-up, intensive screening, and consideration of prophylactic surgery to lower this risk. The limited relevant previous data are not definitive in establishing the prevalence of BRCA1/2 mutations in breast CIS patients, creating uncertainty as to whether referral for cancer risk assessment and genetic testing is appropriate for this group. Therefore, we conducted a cross-sectional analysis of the Myriad Genetics BRCA1/2 database to determine the prevalence of these mutations in breast CIS patients. All statistical tests were 2-sided, and confidence intervals (CI) are reported at the 95% level (α = 0.05). The source population was 64,717 consecutive women who were not Ashkenazi Jewish, underwent BRCA1/2 testing, and provided a personal and family history of invasive breast and ovarian cancer; 7,295 (11.3%) reported a diagnosis of CIS (ductal or lobular) and had an overall 5.9% prevalence of mutated BRCA1/2 (mBRCA). Subgrouped by history (personal or family) of invasive breast and/or ovarian cancer, these CIS patients had the following prevalences of mBRCA: (1) no personal or family history, 2.3%; (2) personal history, 5.2%; (3) family history, 5%; and (4) personal and family history, 10.3%. mBRCA risk was significantly higher in women with early-onset (<50 years old) CIS than with late-onset (≥ 50 years old) CIS [odds ratio (OR) = 1.5; 95% CI = 1.1-2.1). Disease onset at less than 40 years age was associated with an even higher mBRCA risk (OR = 1.8; 95% CI = 1.3-2.3). By far the largest analysis of BRCA1/2 mutation prevalence in non-Ashkenazi Jewish breast CIS patients, this study shows that early-onset CIS is associated with mBRCA1/2 in patients referred for genetic testing. When a family history of breast and/or ovarian cancer are also present, testing women with early-onset CIS may increase both the likelihood of detecting BRCA1/2 mutations and opportunities for carriers to consider additional cancer prevention strategies.