Low-penetrance susceptibility to breast cancer due to CHEK2(*)1100delC in noncarriers of BRCA1 or BRCA2 mutations.

Mutations in BRCA1 and BRCA2 confer a high risk of breast and ovarian cancer, but account for only a small fraction of breast cancer susceptibility. To find additional genes conferring susceptibility to breast cancer, we analyzed CHEK2 (also known as CHK2), which encodes a cell-cycle checkpoint kinase that is implicated in DNA repair processes involving BRCA1 and p53 (refs 3,4,5). We show that CHEK2(*)1100delC, a truncating variant that abrogates the kinase activity, has a frequency of 1.1% in healthy individuals. However, this variant is present in 5.1% of individuals with breast cancer from 718 families that do not carry mutations in BRCA1 or BRCA2 (P = 0.00000003), including 13.5% of individuals from families with male breast cancer (P = 0.00015). We estimate that the CHEK2(*)1100delC variant results in an approximately twofold increase of breast cancer risk in women and a tenfold increase of risk in men. By contrast, the variant confers no increased cancer risk in carriers of BRCA1 or BRCA2 mutations. This suggests that the biological mechanisms underlying the elevated risk of breast cancer in CHEK2 mutation carriers are already subverted in carriers of BRCA1 or BRCA2 mutations, which is consistent with participation of the encoded proteins in the same pathway.

Overexpression of RAD51 occurs in aggressive prostatic cancer.

AIMS: To test the hypothesis that, in a matched series of prostatic cancers, either with or without BRCA1 or BRCA2 mutations, RAD51 protein expression is enhanced in association with BRCA mutation genotypes. METHODS AND RESULTS: RAD51 expression identified immunohistochemically was compared between prostatic cancers occurring in BRCA1 or BRCA2 mutation carriers and controls. RAD51 protein expression in the cytoplasm and nuclei of the benign tissues was significantly less than in the malignant tissues (P < 0.001). In all cancers, cytoplasmic expression of RAD51 was more prevalent and associated with higher Gleason score (P < 0.05) irrespective of BRCA mutational status, than its expression in benign tissues (P < 0.001). Although nuclear immunoreactivity was not observed in BRCA-associated cancers with Gleason score < or =7, it was significantly increased in all other groups of prostatic cancers when compared with benign tissues (P < 0.001). CONCLUSIONS: RAD51 protein is strongly expressed in high-grade prostatic cancers, whether sporadic or associated with BRCA germ-line mutations. Distinct localization of RAD51 between cytoplasm and nucleus, particularly in cancers of Gleason score < or =7, reflects distinct levels of RAD51 regulatory activity, from transcription to DNA repair. This biomarker may be of value in identifying patients requiring urgent treatment at diagnosis as well as in analysing biological mechanisms underlying aggressive phenotype of human prostatic cancer.

Rare germ line CHEK2 variants identified in breast cancer families encode proteins that show impaired activation.

Germ line mutations in CHEK2, the gene that encodes the Chk2 serine/threonine kinase activated in response to DNA damage, have been found to confer an increased risk of some cancers. We have previously reported the presence of the common deleterious 1100delC and four rare CHEK2 mutations in inherited breast cancer. Here, we report that predictions made by bioinformatic analysis on the rare mutations indicate that two of these, delE161 (483-485delAGA) and R117G, are likely to be deleterious. We show that the proteins encoded by 1100delC and delE161 are both unstable and inefficiently phosphorylated at Thr68 in response to DNA damage, a step necessary for the oligomerization of Chk2. Oligomerization is in turn necessary for additional phosphorylation and full activation of the protein. A second rare mutation, R117G, is phosphorylated at Thr68 but fails to show a mobility shift on DNA damage, suggesting that it fails to become further phosphorylated and hence fully activated. Our results indicate that delE161 and R117G encode nonfunctional proteins and are therefore likely to be pathogenic. The findings from the biochemical analysis correlate well with predictions made by bioinformatics analysis. In addition, the results imply that these mutations, as well as 1100delC, cannot act in a dominant-negative manner to cause cancer, and tumorigenesis in association with these mutations may be due to haploinsufficiency.

p53 therapy in a patient with Li-Fraumeni syndrome.

Li-Fraumeni syndrome is an autosomal dominant disorder that greatly increases the risk of developing multiple types of cancer. The majority of Li-Fraumeni syndrome families contain germ-line mutations in the p53 tumor suppressor gene. We describe treatment of a refractory, progressive Li-Fraumeni syndrome embryonal carcinoma with a p53 therapy (Advexin) targeted to the underlying molecular defect of this syndrome. p53 treatment resulted in complete and durable remission of the injected lesion by fluorodeoxyglucose-positron emission tomography scans with improvement of tumor-related symptoms. With respect to molecular markers, the patient's tumor had abnormal p53 and expressed coxsackie adenovirus receptors with a low HDM2 and bcl-2 profile conducive for adenoviral p53 activity. p53 treatment resulted in the induction of cell cycle arrest and apoptosis documented by p21 and cleaved caspase-3 detection. Increased adenoviral antibody titers after repeated therapy did not inhibit adenoviral p53 activity or result in pathologic sequelae. Relationships between these clinical, radiographic, and molecular markers may prove useful in guiding future application of p53 tumor suppressor therapy.

BRCA1/BRCA2 mutation status and analysis of cancer family history in participants of the Royal Marsden Hospital tamoxifen chemoprevention trial.

We have analysed the pedigrees of all 70 women who developed cancer in the Royal Marsden Hospital (RMH) tamoxifen chemoprevention trial, using the Claus model, to assess breast cancer susceptibility heterozygote risk (HR) and screened the entire coding regions of BRCA1 and 2 genes in 62 of these cases. We found a reduced incidence of breast cancers developing on tamoxifen in women who have a lower HR, but not in women with higher HR. There were too few BRCA1/2 mutations (4 cases) to be able to determine the efficacy of tamoxifen by BRCA status. Immunohistochemical analysis showed a significantly lower frequency of median ER (p=0.03) in the cancers developing in tamoxifen-treated patients. These results suggest that tamoxifen is less likely to be effective at reducing breast cancers which are ER negative and also in some individuals at higher HR.

A multicenter study of cancer incidence in CHEK2 1100delC mutation carriers.

The CHEK2 1100delC protein-truncating mutation has a carrier frequency of approximately 0.7% in Northern and Western European populations and confers an approximately 2-fold increased risk of breast cancer. It has also been suggested to increase risks of colorectal and prostate cancer, but its involvement with these or other types of cancer has not been confirmed. The incidence of cancer other than breast cancer in 11,116 individuals from 734 non-BRCA1/2 breast cancer families from the United Kingdom, Germany, Netherlands, and the United States was compared with that predicted by population rates. Relative risks (RR) to carriers and noncarriers were estimated by maximum likelihood, via the expectation-maximization algorithm to allow for unknown genotypes. Sixty-seven families contained at least one tested CHEK2 1100delC mutation carrier. There was evidence of underreporting of cancers in male relatives (422 cancers observed, 860 expected) but not in females (322 observed, 335 expected); hence, we focused on cancer risks in female carriers. The risk of cancers other than breast cancer in female carriers was not significantly elevated, although a modest increase in risk could not be excluded (RR, 1.18; 95% confidence interval, 0.64-2.17). The carrier risk was not significantly raised for any individual cancer site, including colorectal cancer (RR, 1.60; 95% confidence interval, 0.54-4.71). However, between ages 20 to 50 years, the risks of colorectal and lung cancer were both higher in female carriers than noncarriers (P = 0.041 and 0.0001, respectively). There was no evidence of a higher prostate cancer risk in carriers than noncarriers (P = 0.26), although underreporting of male cancers limited our power to detect such a difference. Our results suggest that the risk of cancer associated with CHEK2 1100delC mutations is restricted to breast cancer, although we cannot rule out a small increase in overall cancer risk.

Li-Fraumeni and related syndromes: correlation between tumor type, family structure, and TP53 genotype.

A database has been created to collect information on families carrying a germ-line mutation in the TP53 gene and on families affected with Li-Fraumeni syndromes [Li-Fraumeni syndrome (LFS) and Li-Fraumeni-like syndrome (LFL)]. Data from the published literature have been included. The database is available online at http://www.iarc.fr/p53, as part of the IARC TP53 Database. The analysis of the 265 families/individuals that have been included thus far has revealed several new findings. In classical LFS families with a germ-line TP53 mutation (83 families), the mean age of onset of breast cancer was significantly lower than in LFS families (16 families) without a TP53 mutation (34.6 versus 42.5 years; P = 0.0035). In individuals with a TP53 mutation, a correlation between the genotype and phenotype was found. Brain tumors were associated with missense TP53 mutations located in the DNA-binding loop that contact the minor groove of DNA (P = 0.01), whereas adrenal gland carcinomas were associated with missense mutations located in the loops opposing the protein-DNA contact surface (P = 0.003). Finally, mutations likely to result in a null phenotype (absence of the protein or loss of function) were associated with earlier onset brain tumors (P = 0.004). These observations have clinical implications for genetic testing and tumor surveillance in LFS/LFL families.

A robust method for detecting CHK2/RAD53 mutations in genomic DNA.

While screening for germline CHK2 mutations in cancer cases by heteroduplex CSGE, we observed that additional PCR fragments were generated from the 3' end region of the gene that includes exons 11-14. Direct sequencing of these fragments suggested that homologous loci (possibly pseudogenes) were concomitantly being amplified. Searches of public sequence databases showed that a number of areas of the genome show a high degree of homology to exons 10-14 of the CHK2 gene. The presence of these homologous regions means that standard screening methods for detecting mutations in CHK2, based on PCR of genomic DNA, are prone to error. To circumvent this problem, we have developed a strategy, based on long-range PCR, to screen the functional copy of CHK2. Using this approach it is possible to carry out a comprehensive mutational analysis of CHK2 from genomic DNA.

Analysis of familial male breast cancer for germline mutations in CHEK2.

We have previously shown that the1100delC variant of the cell-cycle-checkpoint kinase gene CHEK2, which is carried by approximately 1% of the population confers a two-fold increase in female breast cancer and a 10-fold increase in male breast cancer. To extend our knowledge on the role of CHEK2 in susceptibility to male breast cancer we have screened a series of 26 breast cancer cases with male representation for germline sequence variation in the CHEK2 gene. One individual was found to harbour the 1100delC variant. No other mutations were identified. Variants other than 1100delC are rare in male breast cancer.

Eligibility for magnetic resonance imaging screening in the United Kingdom: effect of strict selection criteria and anonymous DNA testing on breast cancer incidence in the MARIBS Study.

INTRODUCTION: A UK multicenter study compared the performance of contrast enhanced-magnetic resonance imaging with X-Ray Mammography in women at high-risk of breast cancer commencing in 1997. Selection criteria were used to identify women with at least 0.9% annual risk of breast cancer. METHODS: Women at high breast cancer risk, with a strong family history and/or high probability of a BRCA1/BRCA2/TP53 mutation, were recruited from 22 centers. Those not known as gene carriers were asked to give a blood sample, which was tested anonymously for mutations. Women ages 35 to 49 years were offered annual screening for 2 to 7 years. Study eligibility at entry was assessed retrospectively by detailed examination of pedigrees and overall eligibility accounting for computer risk assessment and mutation results. RESULTS: Seventy-eight of 837 (9%) women entered for screening were ineligible using the strict entry criteria. Thirty-nine cancers were detected in 1,869 women-years in study (incidence 21 per 1,000). Including 3,561 further years follow-up, 28 more breast cancers were identified (12 of 1,000). Incidence rates for 759 eligible women were 22 of 1,000 in study and 13 of 1,000 in total follow-up, compared with 9 of 1,000 and 4 of 1,000, respectively, in 78 ineligible women. Breast cancer rates were higher for BRCA2 than BRCA1 after testing anonymized samples in this selected population at 65 of 1,000 in study and 36 of 1,000 in total follow-up for BRCA2 compared with 44 of 1,000 and 27 of 1,000 for BRCA1. CONCLUSIONS: Strict enforcement of study criteria would have minimally improved the power of the study, whereas testing for BRCA1/2 in advance would have substantially increased the detection rates.

CHK2 kinase: cancer susceptibility and cancer therapy - two sides of the same coin?

In the past decade, CHK2 has emerged as an important multifunctional player in the DNA-damage response signalling pathway. Parallel studies of the human CHEK2 gene have also highlighted its role as a candidate multiorgan tumour susceptibility gene rather than a highly penetrant predisposition gene for Li-Fraumeni syndrome. As discussed here, our current understanding of CHK2 function in tumour cells, in both a biological and genetic context, suggests that targeted modulation of the active kinase or exploitation of its loss in tumours could prove to be effective anti-cancer strategies.