A CHEK2 genetic variant contributing to a substantial fraction of familial breast cancer

Abstract

CHEK2 (previously known as "CHK2") is a cell-cycle-checkpoint kinase that phosphorylates p53 and BRCA1 in response to DNA damage. A protein-truncating mutation, 1100delC in exon 10, which abolishes the kinase function of CHEK2, has been found in families with Li-Fraumeni syndrome (LFS) and in those with a cancer phenotype that is suggestive of LFS, including breast cancer. In the present study, we found that the frequency of 1100delC was 2.0% among an unselected population-based cohort of 1,035 patients with breast cancer. This was slightly, but not significantly (P=.182), higher than the 1.4% frequency found among 1,885 population control subjects. However, a significantly elevated frequency was found among those 358 patients with a positive family history (11/358 [3.1%]; odds ratio [OR] 2.27; 95% confidence interval [CI] 1.11-4.63; P=.021, compared with population controls). Furthermore, patients with bilateral breast cancer were sixfold more likely to be 1100delC carriers than were patients with unilateral cancer (95% CI 1.87-20.32; P=.007). Analysis of the 1100delC variant in an independent set of 507 patients with familial breast cancer with no BRCA1 and BRCA2 mutations confirmed a significantly elevated frequency of 1100delC (28/507 [5.5%]; OR 4.2; 95% CI 2.4-7.2; P=.0002), compared with controls, with a high frequency also seen in patients with only a single affected first-degree relative (18/291 [6.2%]). Finally, tissue microarray analysis indicated that breast tumors from patients with 1100delC mutations show reduced CHEK2 immunostaining. The results suggest that CHEK2 acts as a low-penetrance tumor-suppressor gene in breast cancer and that it makes a significant contribution to familial clustering of breast cancer-including families with only two affected relatives, which are more common than families that include larger numbers of affected women.

Figure 1

Pedigrees of two families with a CHEK2 1100delC germline variant. In family 178 (top), four patients with breast cancer share the mutation, but four unaffected women are also carriers. In family 277 (bottom), the mutation is found only in one patient with breast cancer and her unaffected sister. Prca = prostate cancer; Brca = breast cancer; + = positive for mutation; − = negative for mutation. Numbers followed by “y” represent age at diagnosis, except for two women in family 277, whose age is preceded by “d,” representing age at death.

Figure 2

Immunohistochemical detection of CHEK2 in human breast tissues and tumors on a tissue microarray. Examples include breast carcinomas with normal (panels A and H) or aberrantly reduced (panels B, C, D, E, F, G and I) CHEK2 levels, compared with normal breast tissue control (panel J). The samples shown in panels B, C, and D are from three different tumors with 1100delC, and corresponding detailed staining patterns are documented in panels E, F, and G, respectively. Panel I shows reduced CHEK2 immunostaining in a breast carcinoma wild type for exon 10. The incubation with the DCS-270 antibody and biotin-streptavidin-peroxidase detection was not followed by nuclear counterstaining (Bartkova et al. ; Lukas et al. 2001), to facilitate evaluation of the CHEK2 staining intensity in the nuclei of tumor cells, normal epithelial cells, and stromal cells. Note the reduced staining for CHEK2 in panels B, C, D, E, F, G, and I, compared with normal levels seen in panels A, H, and J. Magnification 30×, in panels A–D, and 120×, in panels E–J.