Spectrum of mutations in BRCA1, BRCA2, CHEK2, and TP53 in families at high risk of breast cancer.

CONTEXT

Genetic testing for inherited mutations in BRCA1 and BRCA2 has become integral to the care of women with a severe family history of breast or ovarian cancer, but an unknown number of patients receive negative (ie, wild-type) results when they actually carry a pathogenic BRCA1 or BRCA2 mutation. Furthermore, other breast cancer genes generally are not evaluated.

OBJECTIVE

To determine the frequency and types of undetected cancer-predisposing mutations in BRCA1, BRCA2, CHEK2, TP53, and PTEN among patients with breast cancer from high-risk families with negative (wild-type) genetic test results for BRCA1 and BRCA2.

DESIGN, SETTING, AND PARTICIPANTS: Between 2002-2005, probands from 300 US families with 4 or more cases of breast or ovarian cancer but with negative (wild-type) commercial genetic test results for BRCA1 and BRCA2 were screened by multiple DNA-based and RNA-based methods to detect genomic rearrangements in BRCA1 and BRCA2 and germline mutations of all classes in CHEK2, TP53, and PTEN.

MAIN OUTCOME MEASURES

Previously undetected germline mutations in BRCA1, BRCA2, CHEK2, TP53, and PTEN that predispose to breast cancer; frequencies of these mutations among families with negative genetic test results.

RESULTS

Of the 300 probands, 52 (17%) carried previously undetected mutations, including 35 (12%) with genomic rearrangements of BRCA1 or BRCA2, 14 (5%) with CHEK2 mutations, and 3 (1%) with TP53 mutations. At BRCA1 and BRCA2, 22 different genomic rearrangements were found, of sizes less than 1 kb to greater than 170 kb; of these, 14 were not previously described and all were individually rare. At CHEK2, a novel 5.6-kb genomic deletion was discovered in 2 families of Czechoslovakian ancestry. This deletion was found in 8 of 631 (1.3%) patients with breast cancer and in none of 367 healthy controls in the Czech and Slovak Republics. For all rearrangements, exact genomic breakpoints were determined and diagnostic primers validated. The 3 families with TP53 mutations included cases of childhood sarcoma or brain tumors in addition to multiple cases of breast cancer.

CONCLUSIONS

The mutational spectra of BRCA1 and BRCA2 include many high-penetrance, individually rare genomic rearrangements. Among patients with breast cancer and severe family histories of cancer who test negative (wild type) for BRCA1 and BRCA2, approximately 12% can be expected to carry a large genomic deletion or duplication in one of these genes, and approximately 5% can be expected to carry a mutation in CHEK2 or TP53. Effective methods for identifying these mutations should be made available to women at high risk.