A deletion in CHEK2 of 5,395 bp predisposes to breast cancer in Poland

Abstract To investigate the contribution of a founder deletion in the CHEK2 gene to the burden of breast cancer in Poland we studied 4,454 women with breast cancer and 5,496 population controls. Cases and controls were genotyped for the presence of a 5,395 bp founder deletion that removes exons 9 and 10 of the CHEK2 gene. This deletion has recently been described in a Czech and Slovak population. The cases and controls had previously been tested for two protein-truncating (IVS2 + 1G > A and 1100delC) and one missense CHEK2 mutation (I157T) which are characteristic for the population. The exons 9 and 10 deletion was present in 0.4% of the controls, in 1.0% (19 of 1,978) of unselected breast cancer cases (OR=2.2; 95% CI: 1.2–4.0; p = 0.01) and in 0.9% (28 of 3,228) of the early-onset cases (OR=2.0; 95% CI: 1.3–1.8; p = 0.02). One of the three truncating CHEK2 mutations (del5395; 1100delC or IVS2 + 1G > A) was seen in 101 of 4,454 (2.3%) cases and in 58 of 5,496 controls (1.1%) (OR=2.2; 95% CI: 1.6–3.0 p < 0.0001). A 5,395 bp founder deletion contributes to the burden of breast cancer in Poland. The deletion was present in 0.9% of the women with breast cancer diagnosed under the age of 51 and in 0.9% of women with breast cancer over the age of 50. This is one of the most common protein-truncating CHEK2 variants in Poland. Overall, 2% of all breast cancers in Poland can be attributed to one of three protein-truncating mutatiosns in CHEK2.     

BARD1 and breast cancer in Poland

Purpose To investigate whether or not a genetic variant in BARD1 (Cys557Ser) contributes to early-onset breast cancer in Poland, or modifies the risk of breast cancer in women with an inherited predisposition to breast cancer. Experimental design We studied 3,188 unselected Polish women with breast cancer and 1,038 healthy controls. All women were genotyped for the BARD1 Cys557Ser variant and for known founder mutations in BRCA1 (three mutations), CHEK2 (four mutations), and NBS1 (one mutation). Results A BARD1 variant was seen in 150 of 3,188 breast cancer cases (4.7%) and in 40 of 1,038 controls (3.8%) (OR = 1.2; 95% CI = 0.9–1.7). The risk associated with the BARD1 variant was not significantly greater in women with familial cancer (OR = 1.5; 95% CI = 0.8–2.7), or with an inherited mutation in BRCA1 (OR = 0.9; 95% CI = 0.4–2.2), CHEK2 (OR = 1.0; 95% CI = 0.5–2.1), or NBS1 (OR = 1.3; 95% CI = 0.2–10.2). Modest associations were observed among the subgroups of women with very early onset breast cancer (OR = 2.9; 95% CI = 1.2–7.1) and with medullary breast cancer (OR = 1.8; 95% CI = 0.9–3.7). Conclusion There was no clear association between the presence of the BARD1 Cys557Ser allele and breast cancer in Poland. Furthermore, the BARD1 Cys557Ser allele does not appear to modify the risk of breast cancers among carriers of BRCA1 mutations, or of other predisposing mutations. The allele may predispose to breast cancers of certain histologic subtypes, but further studies are needed to confirm these findings.     

Constitutional CHEK2 mutations are associated with a decreased risk of lung and laryngeal cancers

Mutations in the CHEK2 gene have been associated with increased risks of breast, prostate and colon cancer. In contrast, a previous report suggests that individuals with the I157T missense variant of the CHEK2 gene might be at decreased risk of lung cancer and upper aero-digestive cancers. To confirm this hypothesis, we genotyped 895 cases of lung cancer, 430 cases of laryngeal cancer and 6391 controls from Poland for four founder alleles in the CHEK2 gene, each of which has been associated with an increased risk of cancer at several sites. The presence of a CHEK2 mutation was protective against both lung cancer [odds ratio (OR) = 0.3; 95% confidence interval (CI) 0.2-0.5; P = 3 x 10(-8)] and laryngeal cancer (OR = 0.6; 95% CI 0.3-0.99; P = 0.05). The basis of the protective effect is unknown, but may relate to the reduced viability of lung cancer cells with a CHEK2 mutation. Lung cancers frequently possess other defects in genes in the DNA damage response pathway (e.g. p53 mutations) and have a high level of genotoxic DNA damage induced by tobacco smoke. We speculate that lung cancer cells with impaired CHEK2 function undergo increased rates of cell death.     

Germline mutations in the CHEK2 kinase gene are associated with an increased risk of bladder cancer

Germline mutations in CHEK2 have been associated with a range of cancer types but little is known about disease risks conveyed by CHEK2 mutations outside of the context of breast and prostate cancer. To investigate whether CHEK2 mutations confer an increased risk of bladder cancer, we genotyped 416 unselected cases of bladder cancer and 3,313 controls from Poland for 4 founder alleles in the CHEK2 gene, each of which has been associated with an increased risk of cancer at other sites. A CHEK2 mutation (all variants combined) was found in 10.6% of the cancer cases and in 5.9% of the controls (OR = 1.9; 95%CI 1.3-2.7; p = 0.0003). We conclude that CHEK2 mutations increase the risk of bladder cancer in the population.     

Breast cancer predisposing alleles in Poland

Summary Mutant alleles of several genes in the DNA repair pathway have been found to predispose women to breast cancer. From a public health perspective, the importance of a given allele in a population is determined by the frequency of the allele and by the relative risk of breast cancer that it confers. In Poland founder alleles of the BRCA1, CHEK2 and NBS1 genes have been associated with an increased risk of breast cancer, but the relative contribution of each of these alleles to the overall breast cancer burden has not yet been determined. We screened 2012 unselected cases of breast cancer and 4000 population controls for 7 different mutations in these genes. Overall, a mutation was found in 12% of the cases and in 6% of the controls. Mutations in BRCA1 and CHEK2 contributed in approximately equal measure to the burden of breast cancer in Poland. A BRCA1 mutation was present in 3% of the cases. The missense BRCA1 mutation C61G was associated with a higher odds ratio for breast cancer (OR=15) than were either of the truncating BRCA1 mutations 4153delA (OR=2.0) and 5382insC (OR=6.2). In contrast, a higher odds ratio was seen for truncating CHEK2 mutations (OR=2.1) than for the missense mutation I157T (OR=1.4). This study suggests that cancer risks may be specific for particular alleles of a susceptibility gene and that these different risks should be taken into account by genetic counselors.     

CDKN2A-positive breast cancers in young women from Poland

Purpose: To investigate the contribution of CDKN2A A148T common variant to early-onset breast cancer in Poland, and to establish the characteristic features of these cancers. Experimental design: We studied 3,069 women diagnosed with breast cancer under the age of 51 and 3,493 population controls. CDKN2A variant were detected using RFLP-PCR and confirmed by genomic sequencing. Clinical and pathological features of CDKN2A-positive cases and CDKN2A-negative cases were compared. Results: A148T variant was identified in 157 of 3,069 women with breast cancer (5.1%). Overall, the odds ratio for early-onset breast cancer, given a CDKN2A variant was 1.4 (95% CI 1.075–1.725; P = 0.012). Breast tumors in women with the CDKN2A variant were more commonly intraductal cancers (DCIS) with micro-invasion (14.8% vs. 8.5%; P = 0.035). Carriers and non-carriers were similar with respect to tumor size, laterality, multicentricity, nodal status, family history and estrogen-receptor status. Conclusion: The CDKN2A A148T variant seems to contribute to early-onset breast cancer in Poland. Breast tumors which arise in carriers of A148T variant appear to be similar to those of breast cancers in the population at large.     

Genetic and functional analysis of CHEK2 (CHK2) variants in multiethnic cohorts

The CHEK2-1100delC mutation is recurrent in the population and is a moderate risk factor for breast cancer. To identify additional CHEK2 mutations potentially contributing to breast cancer susceptibility, we sequenced 248 cases with early-onset disease; functionally characterized new variants and conducted a population-based case-control analysis to evaluate their contribution to breast cancer risk. We identified 1 additional null mutation and 5 missense variants in the germline of cancer patients. In vitro, the CHEK2-H143Y variant resulted in gross protein destabilization, while others had variable suppression of in vitro kinase activity using BRCA1 as a substrate. The germline CHEK2-1100delC mutation was present among 8/1,646 (0.5%) sporadic, 2/400 (0.5%) early-onset and 3/302 (1%) familial breast cancer cases, but undetectable amongst 2,105 multiethnic controls, including 633 from the US. CHEK2-positive breast cancer families also carried a deleterious BRCA1 mutation. 1100delC appears to be the only recurrent CHEK2 mutation associated with a potentially significant contribution to breast cancer risk in the general population. Another recurrent mutation with attenuated in vitro function, CHEK2-P85L, is not associated with increased breast cancer susceptibility, but exhibits a striking difference in frequency across populations with different ancestral histories. These observations illustrate the importance of genotyping ethnically diverse groups when assessing the impact of low-penetrance susceptibility alleles on population risk. Our findings highlight the notion that clinical testing for rare missense mutations within CHEK2 may have limited value in predicting breast cancer risk, but that testing for the 1100delC variant may be valuable in phenotypically- and geographically-selected populations.     

The risk of gastric cancer in carriers of CHEK2 mutations

CHEK2 is a tumor suppressor gene whose functions are central to the induction of cell cycle arrest and apoptosis following DNA damage. Mutations in CHEK2 have been associated with cancers at many sites, including breast and prostate cancers, but the relationship between CHEK2 and gastric cancer has not been extensively studied. In Poland, there are four known founder alleles of CHEK2; three alleles are protein truncating (1100delC, IVS2G>A, del5395) and the other is a missense variant (I157T). We examined the frequencies of four Polish founder mutations in the CHEK2 gene in 658 unselected gastric cancer patients, in 154 familial gastric cancer patients and in 8,302 controls. A CHEK2 mutation was seen in 57 of 658 (8.7 %) unselected patients with gastric cancer compared to 480 of 8,302 (5.8 %) controls (OR 1.6, p = 0.004). A CHEK2 mutation was present in 19 of 154 (12.3 %) familial cases (OR = 2.3, p = 0.001). The odds ratio for early onset (<50 years) gastric cancer was higher (2.1, p = 0.01), than for cases diagnosed at age of 50 or above (OR 1.4, p = 0.05). Truncating mutations of CHEK2 were associated with higher risk (OR = 2.1, p = 0.02) than the missense mutation I157T (OR = 1.4, p = 0.04). CHEK2 mutations predispose to gastric cancer, in particular to young-onset cases.     

CHEK2 mutations and the risk of papillary thyroid cancer

Mutations in the cell cycle checkpoint kinase 2 (CHEK2) tumor suppressor gene are associated with multi‐organ cancer susceptibility including cancers of the breast and prostate. A genetic association between thyroid and breast cancer has been suggested, however little is known about the determinants of this association. To characterize the association of CHEK2 mutations with thyroid cancer, we genotyped 468 unselected patients with papillary thyroid cancer and 468 (matched) cancer‐free controls for four founder mutations of CHEK2 (1100delC, IVS2 + 1G>A, del5395 and I157T). We compared the family histories reported by patients with a CHEK2 mutation to those of non‐carriers. A CHEK2 mutation was seen in 73 of 468 (15.6%) unselected patients with papillary thyroid cancer, compared to 28 of 460 (6.0%) age‐ and sex‐matched controls (OR 3.3; p < 0.0001). A truncating mutation (IVS2 + 1G>A, 1100delC or del5395) was associated with a higher risk of thyroid cancer (OR = 5.7; p = 0.006), than was the missense mutation I157T (OR = 2.8; p = 0.0001). CHEK2 mutation carriers reported a family history of breast cancer 2.2 times more commonly than non‐carriers (16.4% vs.8.1%; p = 0.05). A CHEK2 mutation was found in seven of 11 women (63%) with multiple primary cancers of the breast and thyroid (OR = 10; p = 0.0004). These results suggest that CHEK2 mutations predispose to thyroid cancer, familial aggregations of breast and thyroid cancer and to double primary cancers of the breast and thyroid.     

Pathology of breast cancer in women with constitutional CHEK2 mutations

The power of association studies between polymorphic genetic variants and breast cancer may be enhanced if the cancer subjects are subclassified by histologic subgroup. In this study we classified 482 unselected breast cancers from Szczecin, Poland by histology (ductal, lobular, medullary, other). All women were genotyped for three founder mutations in the CHEK2 gene (1100delC, IVS2 + 1G > A and I157T). There was no significant overall association between CHEK2 and breast cancer (OR = 1.3; p = 0.30), but among those with lobular carcinoma the association with the I157T missense mutation was very strong (OR = 6.6; p > 0.0001). This is the first report to demonstrate that different mutations of the same gene may be associated with specific histologic subtypes of cancer.     

Evaluation of variants in the CHEK2, BRIP1 and PALB2 genes in an Irish breast cancer cohort

It has been proposed that rare variants within the double strand break repair genes CHEK2, BRIP1 and PALB2 predispose to breast cancer. The aim of this study was to evaluate the prevalence of these variants in an Irish breast cancer cohort and determine their contribution to the development of breast cancer in the west of Ireland. We evaluated the presence of CHEK2_1100delC variant in 903 breast cancer cases and 1,016 controls. Six previously described variants within BRIP1 and five within PALB2 were screened in 192 patients with early-onset or familial breast cancer. Where a variant was evident, it was then examined in the remainder of our 711 unselected breast cancer cases. CHEK2_1100delC was found in 5/903 (0.5%) breast cancer cases compared to 1/1016 (0.1%) controls. One mutation at BRIP1 (2392 C>T) was identified in the early-onset/familial cohort. Examination of this variant in the remainder of our cohort (711 cases) failed to identify any additional cases. None of the previously described PALB2 variants were demonstrated in the early-onset/familial cohort. We show evidence of CHEK2_1100delC and BRIP1 2392 C>T within the Irish population. CHEK2_1100delC and BRIP1 mutations incidence in Ireland is similar to that found in other unselected breast cancer cohorts from northern European countries. We found no evidence to suggest that PALB2 mutation is an important breast cancer predisposition gene in this population.     

The CHEK2 I157T variant and breast cancer susceptibility: a systematic review and meta-analysis

Background: The cell cycle checkpoint kinase 2 (CHEK2) gene I157T variant may be associated with anincreased risk of breast cancer, but it is unclear whether the evidence is sufficient to recommend testing for themutation in clinical practice. Materials and Methods: We systematically searched PubMed, Embase, Elsevierand Springer for relevant articles published before Nov 2011. Summary odds ratio (OR) and 95% confidenceinterval (95% CI) incidence rates were calculated using a random-effects model with STATA (version 10.0)software. Results: A total of fifteen case-control studies, including 19,621 cases and 27,001 controls based on thesearch criteria, were included for analysis. A significant association was found between carrying the CHEK2I157T variant and increased risk of unselected breast cancer (OR = 1.48, 95% CI = 1.31–1.66, P < 0.0001), familialbreast cancer (OR = 1.48, 95% CI = 1.16–1.89, P < 0.0001), and early-onset breast cancer (OR = 1.47, 95% CI =1.29–1.66, P < 0.0001). We found an even stronger significant association between the CHEK2 I157T C variantand increased risk of lobular type breast tumors (OR = 4.17, 95% CI = 2.89–6.03, P < 0.0001). Conclusion: Ourresearch indicates that the CHEK2 I157T variant may be another important genetic mutation which increasesrisk of breast cancer, especially the lobular type.     

Prevalence and penetrance of BRCA1 and BRCA2 gene mutations in unselected Ashkenazi Jewish women with breast cancer.

BACKGROUND: Approximately 2.0%-2.5% of Ashkenazi Jewish women carry one of three founding mutations in the BRCA1 and BRCA2 genes, and each mutation is associated with a high lifetime risk of invasive breast cancer. We investigated the extent to which these three mutations contribute to breast cancer incidence in the Ashkenazi Jewish population. METHODS: We ascertained 457 Jewish women with prevalent cases of breast cancer who were unselected for age or family history of the disease; 412 of these women were tested for the three founder mutations (case patients). Control subjects consisted of 360 non-Jewish women with breast cancer (control patients) and 380 healthy Jewish women with no history of cancer (control subjects). RESULTS: Mutations were found in 48 (11.7%) of 412 Jewish case patients. Forty-six of 48 mutations occurred in women with early-onset breast cancer (<50 years) or a history of ovarian or early-onset breast cancer in a first-, second-, or third-degree relative. The estimated penetrance to age 70 years for breast cancer was 59.9% for the BRCA1 gene mutations and 28.3% for the BRCA2 gene mutation. Compared with Jewish control subjects, the relative risk (RR) of breast cancer for first-degree relatives of mutation carriers was 5.16 (95% confidence interval [CI] = 3.14-8. 48), but risk was also increased for relatives of noncarriers (RR = 1.66; 95% CI = 1.18-2.33). The RR of prostate cancer for first-degree relatives of Jewish case patients was 3.36 (95% CI = 1. 49-7.56). CONCLUSIONS: Approximately 12% of breast cancers in the Ashkenazi Jewish population are attributable to mutations in the BRCA1 or BRCA2 gene. Genetic testing may be useful when Jewish women with breast cancer are diagnosed before age 50 years or have a close relative with ovarian or early-onset breast cancer. An association between breast and prostate cancers was observed in our study population.     

CHEK2 mutations and HNPCC‐related colorectal cancer

Recently, the 1100delC variant of cell cycle checkpoint kinase 2 (CHEK2) has been reported to confer a colorectal cancer risk in hereditary non‐polyposis‐colorectal cancer (HNPCC) and HNPCC‐related families in the Netherlands. To investigate whether CHEK2 mutations confer increased cancer risk in HNPCC and HNPCC‐related families in Poland, we genotyped 463 probands from HNPCC and HNPCC‐related families, and 5,496 controls for 4 CHEK2 alleles (1100delC, IVS2+1G>A, del5395, I157T). All 463 probands were screened for mutations in the HNPCC‐related genes MSH2, MLH1 and MSH6. A positive association was observed for HNPCC‐related cancer and the I157T missense CHEK2 mutation (OR = 1.7; p = 0.007), but not for the truncating alleles (OR = 1.0; p = 1.0). The association with the I157T was seen both for the 117 cases who fulfill Amsterdam criteria (OR = 1.9; p = 0.1) and for the 346 cases who do not fulfill the criteria (OR = 1.6; p = 0.03). One hundred forty‐five of the 463 families had a mutation in MSH2, MLH1 or MSH6 (MMR‐positive families). A positive association between the CHEK2 I157T mutation and HNPCC‐related cancer was observed only for MMR‐negative cases (OR = 2.1; p = 0.0004), but not for MMR‐positive cases (OR = 0.8; p = 0.9). The association with I157T was particularly strong for MMR‐negative cases with familial colorectal cancer (2 or more first‐degree relatives affected) (OR = 2.5; p < 0.0001). We conclude that the I157T variant of CHEK2 increases the risk of colorectal cancer among MMR‐negative, HNPCC/HNPCC‐related families in Poland.     

Identification of a Novel BRCA2 and CHEK2 A-C-G-C Haplotype in Turkish Patients Affected with Breast Cancer

Background: Many breast cancers are caused by certain rare and familial mutations in the high or moderatepenetrance genes BRCA1, BRCA2 and CHEK2. The aim of this study was to examine the allele and genotypefrequencies of seven mutations in BRCA1, BRCA2 and CHEK2 genes in breast cancer patients and to investigatetheir isolated and combined associations with breast cancer risk. Methods: We genotyped seven mutations inBRCA1, BRCA2 and CHEK2 genes and then analyzed single variations and haplotype associations in 106 breastcancer patients and 80 healthy controls. Results: We found significant associations in the analyses of CHEK2-1100delC (p=0.001) and BRCA1-5382insC (p=0.021) mutations in breast cancer patients compared to controls.The highest risk was observed among breast cancer patients carrying both CHEK2-1100delC and BRCA2-Met784Val mutations (OR=0.093; 95%CI 0.021-0.423; p=0.001). We identified one previously undescribedBRCA2 and a CHEK2 four-marker haplotype of A-C-G-C which was overrepresented (χ2=7.655; p=0.0057)in the patient group compared to controls. Conclusion: In this study, we identified a previously undescribedBRCA2 and CHEK2 A-C-G-C haplotype in association with the breast cancer in our population. Our resultsfurther suggest that the CHEK2-1100delC mutation in combination with BRCA2-Met784Val may lead to anunexpected high risk which needs to be confirmed in larger cohorts in order to better understand their role inthe development and prognosis of breast cancer.     

A risk of breast cancer in women - carriers of constitutional <Emphasis Type="Italic">CHEK2</Emphasis> gene mutations,originating from the North - Central Poland

Background

Germline mutations of the CHEK2 gene have been reported to be associated with breast cancer. In this study, we analyzed the association of CHEK2 mutations with the risk of development of breast cancer in women of North-Central Poland.

Methods

420 women with breast cancer and 435 controls were tested for three protein truncating (IVS2 + 1G > A, 1100delC, del5395) and one missense (I157T) CHEK2 mutation. IVS2 + 1G > A and I157T mutations were identified by RFLP-PCR, 1100delC variant was analyzed using an ASO-PCR and del5395 mutation by multiplex-PCR. The statistical tests: the odds ratio (OR) and Fisher’s exact test were used.

Results

In 33 out of 420 (7.9%) women consecutively diagnosed with breast cancer, we detected one of four analyzed CHEK2 mutations: I157T, 1100delC, IVS2 + 1G > A or del5395. Together they were not associated with the increased risk of breast cancer (North-Central control group: OR = 1.6, p = 0.124; the general Polish population: OR = 1.4, p = 0.109). This association was only seen for IVS2 + 1G > A mutation (OR = 3.0; p = 0.039). One of the three truncating CHEK2 mutations (IVS2 + 1G > A, 1100delC, del5395) was present in 9 of 420 women diagnosed with breast cancer (2.1%) and in 4 of 121 women (3.3%) with a history of breast cancer in a first- and/or second- degree relatives. Together they were associated with the increased risk of disease in these groups, compared to the general Polish population (OR = 2.1, p = 0.053 and OR = 3.2; p = 0.044, respectively). I157T mutation was detected in 25 of 420 women diagnosed with breast cancer (6.0%) and in 8 of 121 women (6.6%) with a history of breast cancer in first- and/or second- degree relatives. The prevalance of I157T mutation was 4.1% (18/435) in North-Central control group and 4.8% (265/5.496) in the general Polish population. However it was not associated with an increased risk of breast cancer.

Conclusion

Obtained results suggest that CHEK2 mutations could potentially contribute to the susceptibility to breast cancer. The germline mutations of CHEK2, especially the truncating ones confer low-penetrance breast cancer predisposition that contribute significantly to familial clustering of breast cancer at the population level.     

Estrogen Receptor Expression in Benign Breast Ductal Cells Obtained from Random Periareolar Fine Needle Aspiration Correlates with Menopausal Status and Cytomorphology Index Score

Summary We identified 4316 unselected incident cases of early-onset breast cancers (<51 ears of age at diagnosis) in 18 Polish hospitals between 1996 and 2003. We were able to obtain a blood sample for DNA analysis from 3472 of these (80.4%). All cases were tested for the presence of three founder mutations in BRCA1. The proportion of cases with a BRCA1 mutation was 5.7%. The hereditary proportions were higher than this for women with breast cancer diagnosed before age 40 (9%), for women with cancer of medullary or atypical medullary histology (28%), for those with bilateral cancer (29%) or with a family history of breast or ovarian cancer (13%). It is reasonable to offer genetic testing to women with early-onset breast cancer in Poland.     

The CHEK2 gene I157T mutation and other alterations in its proximity increase the risk of sporadic colorectal cancer in the Czech population

Checkpoint kinase 2 (CHEK2) gene codes for an important mediator of DNA damage response pathway. Its mutations increase risk of several types of cancer. We analysed selected CHEK2 mutations in 631 Czech colorectal cancer (CRC) patients. The increased risk of CRC was associated with mutations in CHEK2 gene region involving fork head-associated domain [39/631 (6.2%) cases versus 19/683 (2.8%) controls; odds ratio (OR)=2.3; 95% confidence interval (CI)=1.3-4.0; p=0.003], and with the most frequent I157T mutation [30/631 (4.8%) cases versus 17/683 (2.5%) controls; OR=2.0; 95% CI=1.1-3.6; p=0.03]. Prevalence of 1100delC mutation in CRC patients (4/631) did not differ from that in the control population (2/730; p=0.4). The deletion of 5395 bp was not found in any of the successfully analysed CRC cases. We observed no association of analysed mutations with CRC family history. We conclude that the I157T and other alterations in its proximity predispose to sporadic but not to familial CRC in the Czech population.     

CHEK2 1100delC is not a risk factor for male breast cancer population

Genetic risk factors for male breast cancer (MBC) are poorly understood. High penetrance genes such as BRCA1 or BRCA2 account for only a small proportion of the disease. A 1100delC mutation in CHEK2 (previously known as CHK2), a cell-cycle checkpoint kinase, has been implicated in predisposition of Li-Fraumeni syndrome (LFS) and breast cancer in families suggestive of LFS. This 1100delC mutation has also been shown to confer a 2-fold increase of breast cancer risk in women and a 10-fold increase of risk in men. It was estimated to account for 1% of breast cancers in women and as much as 9% of breast cancers in men at the population level based on analysis of breast cancer families without BRCA1 or BRCA2 mutations. We wanted to evaluate the significance of CHEK2 1100delC in predisposition to MBC by assessing its frequency in a population-based material of 114 Finnish MBC patients. Two patients (1.8%) carried the 1100delC mutation. The mutation frequency among MBC cases was similar to that seen in population controls (26/1885, 1.4%). Our results indicate that CHEK2 1100delC variant does not substantially increase the risk of male breast cancer at the population level. We cannot exclude the fact that a small fraction of hereditary, family-positive male breast cancers could be attributable to CHEK2 mutations.