[CHEK2-mutation in Dutch breast cancer families: expanding genetic testing for breast cancer]

- In the majority of breast cancer families, DNA testing does not show BRCA1 or BRCA2 mutations and the genetic cause of breast cancer remains unexplained. - Routine testing for the CHEK2*1100delC mutation has recently been introduced in breast cancer families in the Netherlands. - The 1100delC mutation in the CHEK2-gene may explain the occurrence of breast cancer in about 5% of non-BRCA1/2 families in the Netherlands. - In the general population the CHEK2*1100delC mutation confers a slightly increased breast cancer risk, but in a familial breast cancer setting this risk is between 35-55% for first degree female carriers. - Female breast cancer patients with the CHEK2*1100delC mutation are at increased risk of contralateral breast cancer and may have a less favourable prognosis. - Female heterozygous CHEK2*1100delC mutation carriers are offered annual mammography and specialist breast surveillance between the ages of 35-60 years.- Prospective research in CHEK2-positive families is essential in order to develop more specific treatment and screening strategies.