The breast cancer low-penetrance allele 1100delC in the CHEK2 gene is not present in Spanish familial breast cancer population

Integrative Analysis of Germline Rare Variants in Clear and Non-clear Cell Renal Cell Carcinoma

Background and objective

Previous germline studies on renal cell carcinoma (RCC) have usually pooled clear and non-clear cell RCCs and have not adequately accounted for population stratification, which might have led to an inaccurate estimation of genetic risk. Here, we aim to analyze the major germline drivers of RCC risk and clinically relevant but underexplored germline variant types.

Methods

We first characterized germline pathogenic variants (PVs), cryptic splice variants, and copy number variants (CNVs) in 1436 unselected RCC patients. To evaluate the enrichment of PVs in RCC, we conducted a case-control study of 1356 RCC patients ancestry matched with 16 512 cancer-free controls using approaches accounting for population stratification and histological subtypes, followed by characterization of secondary somatic events.

Key findings and limitations

Clear cell RCC patients (n = 976) exhibited a significant burden of PVs in VHL compared with controls (odds ratio [OR]: 39.1, p = 4.95e-05). Non-clear cell RCC patients (n = 380) carried enrichment of PVs in FH (OR: 77.9, p = 1.55e-08) and MET (OR: 1.98e11, p = 2.07e-05). In a CHEK2-focused analysis with European participants, clear cell RCC (n = 906) harbored nominal enrichment of low-penetrance CHEK2 variants-p.Ile157Thr (OR: 1.84, p = 0.049) and p.Ser428Phe (OR: 5.20, p = 0.045), while non-clear cell RCC (n = 295) exhibited nominal enrichment of CHEK2 loss of function PVs (OR: 3.51, p = 0.033). Patients with germline PVs in FH, MET, and VHL exhibited significantly earlier age of cancer onset than patients without germline PVs (mean: 46.0 vs 60.2 yr, p < 0.0001), and more than half had secondary somatic events affecting the same gene (n = 10/15, 66.7%). Conversely, CHEK2 PV carriers exhibited a similar age of onset to patients without germline PVs (mean: 60.1 vs 60.2 yr, p = 0.99), and only 30.4% carried somatic events in CHEK2 (n = 7/23). Finally, pathogenic germline cryptic splice variants were identified in SDHA and TSC1, and pathogenic germline CNVs were found in 18 patients, including CNVs in FH, SDHA, and VHL.

Conclusions and clinical implications

This analysis supports the existing link between several RCC risk genes and RCC risk manifesting in earlier age of onset. It calls for caution when assessing the role of CHEK2 due to the burden of founder variants with varying population frequency. It also broadens the definition of the RCC germline landscape of pathogenicity to incorporate previously understudied types of germline variants.

Patient summary

In this study, we carefully compared the frequency of rare inherited mutations with a focus on patients' genetic ancestry. We discovered that subtle variations in genetic background may confound a case-control analysis, especially in evaluating the cancer risk associated with specific genes, such as CHEK2. We also identified previously less explored forms of rare inherited mutations, which could potentially increase the risk of kidney cancer.

Integrative Analysis of Germline Rare Variants in Clear and Non-Clear Cell Renal Cell Carcinoma

IMPORTANCE

RCC encompasses a set of histologically distinct cancers with a high estimated genetic heritability, of which only a portion is currently explained. Previous rare germline variant studies in RCC have usually pooled clear and non-clear cell RCCs and have not adequately accounted for population stratification that may significantly impact the interpretation and discovery of certain candidate risk genes.

OBJECTIVE

To evaluate the enrichment of germline PVs in established cancer-predisposing genes (CPGs) in clear cell and non-clear cell RCC patients compared to cancer-free controls using approaches that account for population stratification and to identify unconventional types of germline RCC risk variants that confer an increased risk of developing RCC.

DESIGN SETTING AND PARTICIPANTS

In 1,436 unselected RCC patients with sufficient data quality, we systematically identified rare germline PVs, cryptic splice variants, and copy number variants (CNVs). From this unselected cohort, 1,356 patients were ancestry-matched with 16,512 cancer-free controls, and gene-level enrichment of rare germline PVs were assessed in 143 CPGs, followed by an investigation of somatic events in matching tumor samples.

MAIN OUTCOMES AND MEASURES

Gene-level burden of rare germline PVs, identification of secondary somatic events accompanying the germline PVs, and characterization of less-explored types of rare germline PVs in RCC patients.

RESULTS

In clear cell RCC (n = 976 patients), patients exhibited significantly higher prevalence of PVs in VHL compared to controls (OR: 39.1, 95% CI: 7.01-218.07, p-value:4.95e-05, q-value:0.00584). In non-clear cell RCC (n = 380 patients), patients carried enriched burden of PVs in FH (OR: 77.9, 95% CI: 18.68-324.97, p-value:1.55e-08, q-value: 1.83e-06) and MET (OR: 1.98e11, 95% CI: 0-inf, p-value: 2.07e-05, q-value: 3.50e-07). In a CHEK2-focused analysis with European cases and controls, clear cell RCC patients (n=906 European patients) harbored nominal enrichment of the previously reported low-penetrance CHEK2 variants, p.Ile157Thr (OR:1.84, 95% CI: 1.00-3.36, p-value:0.049) and p.Ser428Phe (OR:5.20, 95% CI: 1.00-26.40, p-value:0.045) while non-clear cell RCC patients (n=295 European patients) exhibited nominal enrichment of CHEK2 LOF germline PVs (OR: 3.51, 95% CI: 1.10-11.10, p-value: 0.033). RCC patients with germline PVs in FH, MET, and VHL exhibited significantly earlier age of cancer onset compared to patients without any germline PVs in CPGs (Mean: 46.0 vs 60.2 years old, Tukey adjusted p-value < 0.0001), and more than half had secondary somatic events affecting the same gene (n=10/15, 66.7%, 95% CI: 38.7-87.0%). Conversely, patients with rare germline PVs in CHEK2 exhibited a similar age of disease onset to patients without any identified germline PVs in CPGs (Mean: 60.1 vs 60.2 years old, Tukey adjusted p-value: 0.99), and only 30.4% of the patients carried secondary somatic events in CHEK2 (n=7/23, 95% CI: 14.1-53.0%). Finally, rare pathogenic germline cryptic splice variants underexplored in RCC were identified in SDHA and TSC1, and rare pathogenic germline CNVs were found in 18 patients, including CNVs in FH, SDHA, and VHL.

CONCLUSIONS AND RELEVANCE

This systematic analysis supports the existing link between several RCC risk genes and elevated RCC risk manifesting in earlier age of RCC onset. Our analysis calls for caution when assessing the role of germline PVs in CHEK2 due to the burden of founder variants with varying population frequency in different ancestry groups. It also broadens the definition of the RCC germline landscape of pathogenicity to incorporate previously understudied types of germline variants, such as cryptic splice variants and CNVs.

BRCA2 and Other DDR Genes in Prostate Cancer

Germline and somatic aberrations in DNA damage repair (DDR) genes are more prevalent in prostate cancer than previously recognized, with BRCA2 as the most commonly altered gene. Germline mutations in BRCA2 have been linked to poor prognosis when patients are managed under the protocols currently approved for prostate cancer. The impact of germline mutations in other DDR genes beyond BRCA2 remain unclear. Importantly, a quarter of prostate cancer patients identified as germline mutation carriers lack a family history of cancer. The clinical implications of somatic DDR defects are yet to be elucidated. Poly ADP-ribose polymerase (PARP) inhibitors and platinum-based chemotherapy have proven to be effective in the treatment of other tumor types linked to BRCA1 and BRCA2 alterations and several trials are currently evaluating their efficacy in prostate cancer. Here, we summarize the available evidence regarding the prevalence of somatic and germline DDR defects in prostate cancer; their association with clinical outcomes; the trials assessing the efficacy of new therapies that exploit DDR defects in prostate cancer and briefly discuss some uncertainties about the most appropriate management for these patients.

PROREPAIR-B: A Prospective Cohort Study of the Impact of Germline DNA Repair Mutations on the Outcomes of Patients With Metastatic Castration-Resistant Prostate Cancer

PURPOSE

Germline mutations in DNA damage repair (DDR) genes are identified in a significant proportion of patients with metastatic prostate cancer, but the clinical implications of these genes remain unclear. This prospective multicenter cohort study evaluated the prevalence and effect of germline DDR (gDDR) mutations on metastatic castration-resistance prostate cancer (mCRPC) outcomes.

PATIENTS AND METHODS

Unselected patients were enrolled at diagnosis of mCRPC and were screened for gDDR mutations in 107 genes. The primary aim was to assess the impact of ATM/BRCA1/BRCA2/ PALB2 germline mutations on cause-specific survival (CSS) from diagnosis of mCRPC. Secondary aims included the association of gDDR subgroups with response outcomes for mCRPC treatments. Combined progression-free survival from the first systemic therapy (PFS) until progression on the second systemic therapy (PFS2) was also explored.

RESULTS

We identified 68 carriers (16.2%) of 419 eligible patients, including 14 with BRCA2, eight with ATM, four with BRCA1, and none with PALB2 mutations. The study did not reach its primary end point, because the difference in CSS between ATM/BRCA1/BRCA2/PALB2 carriers and noncarriers was not statistically significant (23.3 v 33.2 months; P = .264). CSS was halved in germline BRCA2 (g BRCA2) carriers (17.4 v 33.2 months; P = .027), and g BRCA2 mutations were identified as an independent prognostic factor for CCS (hazard ratio [HR], 2.11; P = .033). Significant interactions between g BRCA2 status and treatment type (androgen signaling inhibitor v taxane therapy) were observed (CSS adjusted P = .014; PFS2 adjusted P = .005). CSS (24.0 v 17.0 months) and PFS2 (18.9 v 8.6 months) were greater in g BRCA2 carriers treated in first line with abiraterone or enzalutamide compared with taxanes. Clinical outcomes did not differ by treatment type in noncarriers.

CONCLUSION

g BRCA2 mutations have a deleterious impact on mCRPC outcomes that may be affected by the first line of treatment used. Determination of g BRCA2 status may be of assistance for the selection of the initial treatment in mCRPC. Nonetheless, confirmatory studies are required before these results can support a change in clinical practice.

CHEK2 Germ Line Mutations are Lacking among Familial and Sporadic Breast Cancer Patients in Rwanda

Worldwide, breast cancer is the most frequent neoplasm and the second leading cause of cancer death among females. It dominates in both developed and developing countries and represents a major public health problem. The etiology is multifactorial and involves exogenous agents as well as endogenous factors. Although they account for only a small fraction of the breast cancer burden, mutations in the BRCA1 and BRCA2 genes are known to confer a high risk predisposition. Mutations in moderate/low-penetrance genes may also contribute to breast cancer risk. Previous studies have shown that mutations in the CHEK2 gene are involved in breast cancer susceptibility due to its impact on DNA repair processes and replication checkpoints. This study was conducted to evaluate the frequencies of three germline mutations in CHEK2 gene (c.1100delC, R145W and I157T) in breast cancers in Rwanda. Using direct DNA sequencing, we analyzed 41 breast cancer patients and 42 normal breast controls but could not detect any positives. CHEK2 mutations may be a rare event in Rwandan population and may only play a minor if an role in breast cancer predisposition among familial and sporadic cases.

Current perspectives on CHEK2 mutations in breast cancer

Checkpoint kinase 2 (CHEK2) is a serine/threonine kinase which is activated upon DNA damage and is implicated in pathways that govern DNA repair, cell cycle arrest or apoptosis in response to the initial damage. Loss of kinase function has been correlated with different types of cancer, mainly breast cancer. CHEK2 functionality is affected by different missense or deleterious mutations. CHEK2*1100delC and I157T are most studied in populations all over the world. Although these variants have been identified in patients with breast cancer, their frequency raises doubts about their importance as risk factors. The present article reviews the recent advances in research on CHEK2 mutations, focusing on breast cancer, based on the latest experimental data.

An association study between CHEK2 gene mutations and susceptibility to breast cancer

CHEK2 gene is known as a tumor suppressor gene in breast cancer (BC), which plays a role in DNA repair. The germ line mutations in CEHK2 have been associated with different types of cancer. The present study was aimed at studying the association between CHEK2 mutations and BC. Peripheral blood was collected from patients into a test tube containing EDTA, and DNA was extracted from blood samples. Then, we analyzed mutations including 1100delc, IVS2+1>A, del5395bp, and I157T within CHEK2 gene in patients with BC and 100 normal healthy controls according to PCR-RFLP, allelic specific PCR, and multiplex-PCR. Although IVS2+1G>A mutation within CHEK2 gene was found in two BC patients, other defined mutants were not detected. For the first time, we identified CHEK2 IVS2+1G>A mutation, one out of four different CHEK2 alterations in two Iranian BC patients (2%). Also, our results showed that CHEK2 1100elC, del5395bp, and I157T mutations are not associated with genetic susceptibility for BC among Iranian population.

Routine use of gene panel testing in hereditary breast cancer should be performed with caution

Breast cancer is the most frequent cancer occurring in women. Ten percent of these cancers are considered hereditary. Among them, 30% are attributed to germline mutations in the tumor suppressor genes BRCA1 and BRCA2. Other genes of lower penetrance are also known, explaining together up to 40% of the hereditary risk of breast cancer. New techniques, such as next-generation sequencing, allow the simultaneous analysis of multiple genes in a cost-effective way. As a logical consequence, gene panel testing is entering clinical practice with the promise of personalized care. We however advocate that gene panel testing is not ready for non-specialist clinical use, as it generates many variants of unknown significance and includes more genes than are presently considered clinically useful. We hereby review the data for each gene that can change the risk management of patients carrying a pathogenic variant.

Association between CHEK2 H371Y mutation and response to neoadjuvant chemotherapy in women with breast cancer

Background

Our previous study suggested that the recurrent CHEK2 H371Y mutation is a novel pathogenic mutation that confers an increased risk of breast cancer. The purpose of this study was to investigate whether breast cancer patients with CHEK2 H371Y mutation were more likely to respond to neoadjuvant chemotherapy.

Methods

We screened a cohort of 2334 Chinese women with operable primary breast cancer who received a neoadjuvant chemotherapy regimen for CHEK2 H371Y germline mutations. Pathologic complete response (pCR) was defined as the absence of tumor cells in the breast after the completion of neoadjuvant chemotherapy.

Results

Thirty-nine patients (1.7%) with CHEK2 H371Y germline mutation were identified in this cohort of 2334 patients. CHEK2 H371Y mutation carriers had a significantly higher pCR rate than non-carriers (33.3% versus 19.5%, P = 0.031) in the entire study population, and CHEK2 H371Y mutation-positive status remained an independent favorable predictor of pCR in a multivariate analysis (odds ratio [OR] = 3.01; 95% confidence interval [CI]: 1.34- 6.78, P = 0.008). CHEK2 H371Y carriers had a slightly worse distant recurrence-free survival than non-carriers (adjusted hazard ratio [HR] =1.24, 95% CI: 0.59-2.63).

Conclusions

CHEK2 H371Y mutation carriers are more likely to respond to neoadjuvant chemotherapy than are non-carriers.

CHEK2 c.1100delC allele is rarely identified in Greek breast cancer cases

The CHEK2 gene encodes a protein kinase that plays a crucial role in maintenance of genomic integrity and the DNA repair mechanism. CHEK2 germline mutations are associated with increased risk of breast cancer and other malignancies. From a clinical perspective, the most significant mutation identified is the c.1100delC mutation, which is associated with an approximately 25% lifetime breast cancer risk. The distribution of this mutation shows wide geographical variation; it is more prevalent in the Northern European countries and less common, or even absent, in Southern Europe. In order to estimate the frequency of the CHEK2 c.1100delC mutation in Greek breast cancer patients, we genotyped 2,449 patients (2,408 females and 41 males), which was the largest series ever tested for c.1100delC. The mean age of female and male breast cancer diagnosis was 49 and 59 years, respectively. All patients had previously tested negative for the Greek BRCA1 founder and recurrent mutations. The CHEK2 c.1100delC mutation was detected in 0.16% (4 of 2,408) of females, all of whom were diagnosed with breast cancer before the age of 50 years. Only one c.1100delC carrier was reported with breast cancer family history. The present study indicates that the CHEK2 c.1100delC mutation does not contribute substantially to hereditary breast cancer in patients of Greek descent.

The CHEK2 1100delC allelic variant is not present in familial and sporadic breast cancer cases from Moroccan population

Purpose

The cell-cycle checkpoint kinase 2 (CHEK2) is an important signal transducer of cellular responses to DNA damage, whose defects has been associated with increased risk for breast cancer. The CHEK2 1100delC mutation has been reported to confer a twofold increased risk of breast cancer among carriers. The frequency of the mutation varies among populations. The highest frequency has been described in Northern and Eastern European countries. However, the 1100delC mutation has been investigated in different case-control studies and none in Moroccan population. The aim of this study was to evaluate the prevalence of this variant and determine its contribution to the development of breast cancer in sporadic cases and also in members of breast cancer families who tested negative or positive for a deleterious mutation in BRCA1/BRCA2.

Methods

In this case-control study we performed the CHEK2 1100delC mutation analysis by ASO-PCR in 134 breast cancer patients and 114 unaffected control individuals. Most of these families had several cases of breast cancer or ovarian cancer (or both).

Results

No CHEK2 1100delC mutations were detected in any of 134 individuals, including 59 women diagnosed with breast cancer at an early age (<40 years), 10 women with bilateral breast cancer, and 6 women with ovarian cancer.

Conclusion

Our preliminary genetic analysis are consistent with the reported very low frequency of CHEK2 1100delC mutation in North American populations (compared with Northern Europe), rendering CHEK2 1100delC such as an unlikely to be major breast cancer susceptibility genes.

Low prevalence of CHEK2 gene mutations in multiethnic cohorts of breast cancer patients in Malaysia

CHEK2 is a protein kinase that is involved in cell-cycle checkpoint control after DNA damage. Germline mutations in CHEK2 gene have been associated with increase in breast cancer risk. The aim of this study is to identify the CHEK2 gene germline mutations among high-risk breast cancer patients and its contribution to the multiethnic population in Malaysia. We screened the entire coding region of CHEK2 gene on 59 high-risk breast cancer patients who tested negative for BRCA1/2 germline mutations from UKM Medical Centre (UKMMC), Hospital Kuala Lumpur (HKL) and Hospital Putrajaya (HPJ). Sequence variants identified were screened further in case-control cohorts consisting of 878 unselected invasive breast cancer patients (180 Malays, 526 Chinese and 172 Indian) and 270 healthy individuals (90 Malays, 90 Chinese and 90 Indian). By screening the entire coding region of the CHEK2 gene, two missense mutations, c.480A>G (p.I160M) and c.538C>T (p.R180C) were identified in two unrelated patients (3.4%). Further screening of these missense mutations on the case-control cohorts unveiled the variant p.I160M in 2/172 (1.1%) Indian cases and 1/90 (1.1%) Indian control, variant p.R180C in 2/526 (0.38%) Chinese cases and 0/90 Chinese control, and in 2/180 (1.1%) of Malay cases and 1/90 (1.1%) of Malay control. The results of this study suggest that CHEK2 mutations are rare among high-risk breast cancer patients and may play a minor contributing role in breast carcinogenesis among Malaysian population.

CHEK2 (∗) 1100delC Mutation and Risk of Prostate Cancer

Although the causes of prostate cancer are largely unknown, previous studies support the role of genetic factors in the development of prostate cancer. CHEK2 plays a critical role in DNA replication by responding to double-stranded breaks. In this review, we provide an overview of the current knowledge of the role of a genetic variant, 1100delC, of CHEK2 on prostate cancer risk and discuss the implication for potential translation of this knowledge into clinical practice. Currently, twelve articles that discussed CHEK2 (∗)1100delC and its association with prostate cancer were identified. Of the twelve prostate cancer studies, five studies had independent data to draw conclusive evidence from. The pooled results of OR and 95% CI were 1.98 (1.23-3.18) for unselected cases and 3.39 (1.78-6.47) for familial cases, indicating that CHEK2 (∗)1100delC mutation is associated with increased risk of prostate cancer. Screening for CHEK2(∗)1100delC should be considered in men with a familial history of prostate cancer.

Constitutional CHEK2 mutations are infrequent in early-onset and familial breast/ovarian cancer patients from Pakistan

Background

Less than 20% of Pakistani women with early-onset or familial breast/ovarian cancer harbor germ line mutations in the high-penetrance genes BRCA1, BRCA2 and TP53. Thus, mutations in other genes confer genetic susceptibility to breast cancer, of which CHEK2 is a plausible candidate. CHEK2 encodes a checkpoint kinase, involved in response to DNA damage.

Methods

In the present study we assessed the prevalence of CHEK2 germ line mutations in 145 BRCA1/2-negative early-onset and familial breast/ovarian cancer patients from Pakistan (Group 1). Mutation analysis of the complete CHEK2 coding region was performed using denaturing high-performance liquid chromatography analysis, followed by DNA sequencing of variant fragments.

Results

Two potentially deleterious missense mutations, c.275C>G (p.P92R) and c.1216C>T, (p.R406C), were identified (1.4%). The c.275C>G mutation is novel and has not been described in other populations. It was detected in a 30-year-old breast cancer patient with a family history of breast and multiple other cancers. The c.1216C>T mutation was found in a 34-year-old ovarian cancer patient from a family with two breast cancer cases. Both mutations were not detected in 229 recently recruited BRCA1/2-negative high risk patients (Group 2).

Conclusion

Our findings suggest that CHEK2 mutations may not contribute significantly to breast/ovarian cancer risk in Pakistani women.

RAD50 and NBS1 are not likely to be susceptibility genes in Chinese non-BRCA1/2 hereditary breast cancer

Deleterious mutations in several genes that are involved in repair of damage to DNA have been associated with an increased risk of breast cancer. Recent studies have shown sequence variants in two such genes, RAD50 and NBS1, which can be predisposed to breast cancer. The aim of this study is to elucidate the contribution of RAD50 and NBS1 germline mutations to the etiology of non-BRCA1/2 hereditary breast cancer in China. We conducted a mutational analysis of RAD50 and NBS1 in genomic DNA from 384 Chinese women with early-onset breast cancer and/or affected relatives. All the coding exons and adjacent intronic splice junction rejoins of RAD50 and NBS1 were screened using PCR-DHPLC and DNA sequencing analysis. Among all cases, no obviously deleterious mutations were observed in RAD50; one synonymous change c.102G>A at codon 34 and one single nucleotide polymorphism IVS9 + 19C>T were identified in NBS1. Furthermore, there was no remarkable difference in the allele frequency of NBS1 c.553G>C (E185Q) between cases (172/384) and controls (182/420). Our results exclude the possible role of RAD50 and NBS1 in familial breast cancer predisposition in Chinese women, and there is no evidence for the recommendation of RAD50 and NBS1 for genetic testing in China.

CHEK2 1100delC, IVS2+1G>A and I157T mutations are not present in colorectal cancer cases from Turkish population

BACKGROUND

The cell cycle checkpoint kinase 2 (CHEK2) protein participates in the DNA damage response in many cell types. Germline mutations in CHEK2 (1100delC, IVS2+1G>A and I157T) have been impaired serine/threonine kinase activity and associated with a range of cancer types. This hospital-based case-control study aimed to investigate whether CHEK2 1100delC, IVS2+1G>A and I157T mutations play an important role in the development of colorectal cancer (CRC) in Turkish population.

METHODS

A total of 210 CRC cases and 446 cancer-free controls were genotyped for CHEK2 mutations by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) and allele specific-polymerase chain reaction (AS-PCR) methods.

RESULTS

We did not find the CHEK2 1100delC, IVS2+1G>A and I157T mutations in any of the Turkish subjects.

CONCLUSION

Our result demonstrate for the first time that CHEK2 1100delC, IVS2+1G>A and I157T mutations have not been agenetic susceptibility factor for CRC in the Turkish population. Overall, our data suggest that genotyping of CHEK2 mutations in clinical settings in the Turkish population should not be recommended. However, independent studies are need to validate our findings in a larger series, as well as in patients of different ethnic origins.

CHEK2 contribution to hereditary breast cancer in non-BRCA families

Background

Mutations in the BRCA1 and BRCA2 genes are responsible for only a part of hereditary breast cancer (HBC). The origins of "non-BRCA" HBC in families may be attributed in part to rare mutations in genes conferring moderate risk, such as CHEK2, which encodes for an upstream regulator of BRCA1. Previous studies have demonstrated an association between CHEK2 founder mutations and non-BRCA HBC. However, very few data on the entire coding sequence of this gene are available.

Methods

We investigated the contribution of CHEK2 mutations to non-BRCA HBC by direct sequencing of its whole coding sequence in 507 non-BRCA HBC cases and 513 controls.

Results

We observed 16 mutations in cases and 4 in controls, including 9 missense variants of uncertain consequence. Using both in silico tools and an in vitro kinase activity test, the majority of the variants were found likely to be deleterious for protein function. One variant present in both cases and controls was proposed to be neutral. Removing this variant from the pool of potentially deleterious variants gave a mutation frequency of 1.48% for cases and 0.29% for controls (P = 0.0040). The odds ratio of breast cancer in the presence of a deleterious CHEK2 mutation was 5.18.

Conclusions

Our work indicates that a variety of deleterious CHEK2 alleles make an appreciable contribution to breast cancer susceptibility, and their identification could help in the clinical management of patients carrying a CHEK2 mutation.

Risk of Breast Cancer in Women With a CHEK2 Mutation With and Without a Family History of Breast Cancer

Purpose

To estimate the risk of breast cancer in a woman who has a CHEK2 mutation depending on her family history of breast cancer.

Patients and Methods

Seven thousand four hundred ninety-four BRCA1 mutation–negative patients with breast cancer and 4,346 control women were genotyped for four founder mutations in CHEK2 (del5395, IVS2+1G>A, 1100delC, and I157T).

Results

A truncating mutation (IVS2+1G>A, 1100delC, or del5395) was present in 227 patients (3.0%) and in 37 female controls (0.8%; odds ratio [OR], 3.6; 95% CI, 2.6 to 5.1). The OR was higher for women with a first- or second-degree relative with breast cancer (OR, 5.0; 95% CI, 3.3 to 7.6) than for women with no family history (OR, 3.3; 95% CI, 2.3 to 4.7). If both a first- and second-degree relative were affected with breast cancer, the OR was 7.3 (95% CI, 3.2 to 16.8). Assuming a baseline risk of 6%, we estimate the lifetime risks for carriers of CHEK2 truncating mutations to be 20% for a woman with no affected relative, 28% for a woman with one second-degree relative affected, 34% for a woman with one first-degree relative affected, and 44% for a woman with both a first- and second-degree relative affected.

Conclusion

CHEK2 mutation screening detects a clinically meaningful risk of breast cancer and should be considered in all women with a family history of breast cancer. Women with a truncating mutation in CHEK2 and a positive family history of breast cancer have a lifetime risk of breast cancer of greater than 25% and are candidates for magnetic resonance imaging screening and for tamoxifen chemoprevention.

Absence of CHEK2*1100delC mutation in families with hereditary breast cancer in North America

The CHEK2*1100delC mutation has been reported to confer a twofold increased risk of breast cancer among carriers. The frequency of the mutation varies among populations. The highest frequency has been described in Northern and Eastern European countries; the frequency may be much lower in North America. In this study, our aim was to determine the frequency of CHEK2*1100delC in members of breast cancer families who tested negative for a deleterious mutation in BRCA1/2 at the University of Michigan Comprehensive Cancer Center. We genotyped 102 members from 90 families for CHEK2*1100delC. Most of these families had several cases of breast cancer or ovarian cancer (or both), as well as multiple members with other cancer types in a single lineage. No CHEK2*1100delC mutations were detected in any of the 102 individuals, including 51 women diagnosed with breast cancer at an early age (<45 years), 8 women with bilateral breast cancer, 3 men with breast cancer, and 8 women with ovarian cancer. Our data are consistent with the reported very low frequency of CHEK2*1100delC mutations in North American populations (compared with Northern Europe), rendering CHEK2*1100delC such an unlikely culprit in BRCA1/2 negative families that routine testing of these families appears unwarranted.

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.

Pitfalls and Caveats in BRCA Sequencing

Between 5 and 10% of breast cancer cases are considered to result from hereditary predisposition. Germ-line mutations in BRCA1 and BRCA2 are responsible for an inherited predisposition of breast and ovarian cancer. Direct nucleotide sequencing is considered the gold standard technique for mutation detection for genes such as BRCA1 and BRCA2. In many laboratories that analyze BRCA1 and BRCA2, previous to direct sequencing, screening techniques to identify sequence variants in the PCR amplicons are performed. The mutations detected in these genes may be frameshift mutations (insertions or deletions), nonsense mutations, or missense mutations. The clinical interpretation of the mutation as the cause of the disease may be difficult to establish in the case of missense mutations. Only in 30-70% of the families in which a hereditary component is suspected, a mutation in BRCA1 and/or BRCA2 is detected. Negative results may be due to: wrong selection of the proband; mutations in the regulatory portion of the genes; gene silencing due to epigenetic phenomena; or large genomic rearrangements that produce deletions of whole exons. Another possibility that explains the lack of detection of alterations in BRCA1 or BRCA2 is the presence of mutations in undiscovered genes or in genes that interact with BRCA1 and/or BRCA2, which may be low-penetrance genes, like CHEK2.

CHEK2*1100delC does not contribute to risk to breast cancer among Malay, Chinese and Indians in Malaysia

A truncating mutation (1100delC) in the cell cycle checkpoint kinase-2 gene, CHEK2, has been identified as a risk factor for familial and sporadic breast cancer in some Northern and Western European populations. However, the prevalence of CHEK2*1100delC in breast cancer appears to be population dependent. We analysed the prevalence of CHEK2*1100delC in 668 breast cancer cases, of which 542 were invasive breast cancers, from a hospital-based cohort of breast cancer patients from Kuala Lumpur, Malaysia. The variant was not found in any patients in this cohort, suggesting that CHEK2*1100delC is rare in our population, and unlikely to contribute significantly to risk to breast cancer among the Malay, Chinese and Indian ethnic groups in Malaysia. This suggests that screening for this allele should not be routinely conducted in Malaysia.

The contribution of CHEK2 to the TP53-negative Li-Fraumeni phenotype

BACKGROUND

CHEK2 has previously been excluded as a major cause of Li-Fraumeni syndrome (LFS). One particular CHEK2 germline mutation, c.1100delC, has been shown to be associated with elevated breast cancer risk. The prevalence of CHEK2*1100delC differs between populations and has been found to be relatively high in the Netherlands. The question remains nevertheless whether CHEK2 germline mutations contribute to the Li-Fraumeni phenotype.

METHODS

We have screened 65 Dutch TP53-negative LFS/LFL candidate patients for CHEK2 germline mutations to determine their contribution to the LFS/LFL phenotype.

RESULTS

We identified six index patients with a CHEK2 sequence variant, four with the c.1100delC variant and two sequence variants of unknown significance, p.Phe328Ser and c.1096-?_1629+?del.

CONCLUSION

Our data show that CHEK2 is not a major LFS susceptibility gene in the Dutch population. However, CHEK2 might be a factor contributing to individual tumour development in TP53-negative cancer-prone families.

Breast cancer susceptibility: current knowledge and implications for genetic counselling

Breast cancer is the most common malignancy in women in the Western world. Except for the high breast cancer risk in BRCA1 and BRCA2 mutation carriers as well as the risk for breast cancer in certain rare syndromes caused by mutations in TP53, STK11, PTEN, CDH1, NF1 or NBN, familial clustering of breast cancer remains largely unexplained. Despite significant efforts, BRCA3 could not be identified, but several reports have recently been published on genes involved in DNA repair and single nucleotide polymorphisms (SNPs) associated with an increased breast cancer risk. Although candidate gene approaches demonstrated moderately increased breast cancer risks for rare mutations in genes involved in DNA repair (ATM, CHEK2, BRIP1, PALB2 and RAD50), genome-wide association studies identified several SNPs as low-penetrance breast cancer susceptibility polymorphisms within genes as well as in chromosomal loci with no known genes (FGFR2, TOX3, LSP1, MAP3K1, TGFB1, 2q35 and 8q). Some of these low-penetrance breast cancer susceptibility polymorphisms also act as modifier genes in BRCA1/BRCA2 mutation carriers. This review not only outlines the recent key developments and potential clinical benefit for preventive management and therapy but also discusses the current limitations of genetic testing of variants associated with intermediate and low breast cancer risk.

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.

Discovering interactions among BRCA1 and other candidate genes associated with sporadic breast cancer

Analysis of a subset of case-control sporadic breast cancer data, [from the National Cancer Institute's Cancer Genetic Markers of Susceptibility (CGEMS) initiative], focusing on 18 breast cancer-related genes with 304 SNPs, indicates that there are many interesting interactions that form two- and three-way networks in which BRCA1 plays a dominant and central role. The apparent interactions of BRCA1 with many other genes suggests the conjecture that BRCA1 serves as a protective gene and that some mutations in it or in related genes may prevent it from carrying out this protective function even if the patients are not carriers of known cancer-predisposing BRCA1 mutations. The method of analysis features the evaluation of the effect of a gene by averaging the effects of the SNPs covered by that gene. Marginal methods that test one gene at a time fail to show any effect. That may be related to the fact that each of these 18 genes adds very little to the risk of cancer. Analysis that relates the ratio of interactions to the maximum of the first-order effects discovers significant gene pairs and triplets.

Breast cancer low-penetrance allele 1100delC in the CHEK2 gene: not present in the Chinese familial breast cancer population

INTRODUCTION

The 1100delC CHEK2 allele has been associated with a 1.4-to 4.7-fold increased risk of breast cancer in women carrying this mutation. Our study investigated the frequency of this allele in a Chinese population.

METHODS

Using touchdown polymerase chain reaction, we sequenced the CHEK2.1100delC mutation in 74 breast cancer patients with a family history of breast cancer and 50 control subjects.

RESULTS

We did not find the CHEK2.1100delC mutation in any of the Chinese subjects. However, another missense mutation, 1111C>T (His371Tyr), was found in a familial breast cancer patient, but not in any other subjects.

CONCLUSION

The CHEK2.1100delC mutation may be a rare variant in Chinese populations and may not contribute to predisposition for familial breast cancer in China. However, there may be an association between genetic susceptibility to breast cancer in China and the variant 1111C>T.

Risk for contralateral breast cancer among carriers of the CHEK2*1100delC mutation in the WECARE Study

The protein encoded by the CHEK2 gene is involved in cellular repair of DNA damage. The truncating mutation, CHEK2^*1100delC, seems to increase the risk for breast cancer. We investigated whether the CHEK2^*1100delC mutation carrier status increases the risk for asynchronous contralateral breast cancer (CBC) and whether it interacts with radiation therapy (RT) or chemotherapy in regard to CBC risk. The germline mutation frequency was assessed in 708 women with CBC and 1395 women with unilateral breast cancer (UBC) in the Women's Environment, Cancer and Radiation Epidemiology (WECARE) Study whose first primary breast cancer was diagnosed before age 55 years and during 1985–1999. Seven women with CBC (1.0%) and 10 women with UBC (0.7%) were CHEK2^*1100delC variant carriers (rate ratio (RR)=1.8, 95% confidence interval (CI)=0.6–5.4 for CBC vs UBC). Carriers who received RT for their first breast cancer, compared with non-carriers not treated with RT, had an RR of developing CBC of 2.6 (95% CI=0.8–8.7). We found no significant associations between the CHEK2^*1100delC mutation and CBC overall or among those treated with RT. However, the sampling variability was such that modest increases in risk could not be excluded. Nonetheless, because this is a rare mutation, it is unlikely to explain a major fraction of CBC in the population.

CHEK2*1100delC Genotyping for Clinical Assessment of Breast Cancer Risk: Meta-Analyses of 26,000 Patient Cases and 27,000 Controls

Purpose

CHEK2*1100delC heterozygosity may be associated with an increased risk of breast cancer; however, it is unclear whether the evidence is sufficient to recommend genotyping in clinical practice.

Patients and Methods

We identified studies on CHEK2*1100delC heterozygosity and the risk of unselected, early-onset, and familial breast cancer through comprehensive, computer-based searches of PubMed, EMBASE, and Web of Science. Aggregated risk estimates were compared with previous estimates for BRCA1 and BRCA2 mutation heterozygotes.

Results

By using fixed-effect models for CHEK2*1100delC heterozygotes versus noncarriers, we found aggregated odds ratios of 2.7 (95% CI, 2.1 to 3.4) for unselected breast cancer, 2.6 (95% CI, 1.3 to 5.5) for early-onset breast cancer, and 4.8 (95% CI, 3.3 to 7.2) for familial breast cancer. For familial breast cancer, this corresponds to a cumulative risk of breast cancer at age 70 years in CHEK2*1100delC heterozygotes of 37% (95% CI, 26% to 56%), which compares with similar previous estimates of 57% (95% CI, 47% to 66%) for BRCA1 mutation heterozygotes and 49% (95% CI, 40% to 57%) for BRCA2 mutation heterozygotes.

Conclusion

These meta-analyses emphasize that CHEK2*1100delC is an important breast cancer–predisposing gene, which increases the risk three- to five-fold. Because the cumulative risk of breast cancer at age 70 years among familial patient cases for CHEK2*1100delC heterozygotes is almost as high as that for BRCA1 and BRCA2 mutation heterozygotes, genotyping for CHEK2*1100delC should be considered together with BRCA1 and BRCA2 mutation screening in women with a family history of breast cancer.

The CHEK2 1100delC mutation is not present in Korean patients with breast cancer cases tested for BRCA1 and BRCA2 mutation

The germline CHEK2 1100delC mutation is a low penetrance breast cancer susceptibility allele, frequently observed in patient with family history of breast cancer and/or young age and the frequency varied according to race or ethnicity. In this study, we evaluated the significance of CHEK2 1100delC in predisposition to breast cancer by assessing its frequency in a material of 493 Korean breast cancer patients who had been screened for BRCA1 and BRCA2 mutations (42 patients had deleterious mutation of BRCA1/2). Mutation detection of CHEK2 1100delC was based upon analysis of primer extension products generated for previously amplified genomic DNA using a chip based MALDI-TOP mass spectrometry platform. After overall measurement automatically, assays which had bad peaks were checked again manually. None of the 493 Korean patients with breast cancer who were candidate for BRCA1 and BRCA2 test carried the 1100delC mutation observed in Caucasians with limited frequency. In the previous studies, we observed higher or comparable prevalence of BRCA1 and BRCA2 mutations in Korean patients with breast cancer compared to Caucasian breast cancer population. In the present study, we evaluated the role of a CHEK2 1100delC as a susceptibility mutation of breast cancer in the Korean population. However, our results suggest that this mutation is absent or may be very infrequent in Korean patients with breast cancer who have high risk of BRCA1 and BRCA2 mutation, making its screening irrelevant from the practical point view.

Analysis of CHEK2 FHA domain in Czech patients with sporadic breast cancer revealed distinct rare genetic alterations

The CHEK2 gene mutations I157T (c.470T>C) and IVS2+1G>A affecting the forkhead-associated domain (FHA) have been shown to increase the risk of breast cancer development in several populations. We analyzed the CHEK2 gene segment coding for FHA domain in 673 unselected breast cancer patients and 683 controls from the Czech Republic using the denaturant high-performance liquid chromatography. The found frequency of predominant FHA alteration I157T did not differ between breast cancer patients (19/673; 2.82%) and controls (17/683; 2.49%; P=0.71). Besides this mutation we characterized another nine alterations-six located within FHA coding sequence and three occurring in introns 1 or 2). Eight variants occurred once each in patients with breast cancer and two were present in controls. Three alterations found in breast cancer patients were novel missense variants (Y159H, T172A, and L174F) affecting highly conservative residues in FHA domain. Despite the lack of association of I157T mutation with breast cancer development in our population we deduced that the FHA domain is the subject of rare population-specific alterations that might modify risk of various cancers.

CHEK2 1100delC is prevalent in Swedish early onset familial breast cancer

Background

A truncating variant, 1100delC, in check point-kinase CHEK2, has been identified as a risk factor for familial and sporadic breast cancer. The prevalence in healthy non-breast cancer cases is low and varies between populations.

Methods

We analyzed the prevalence of CHEK2 1100delC in 763 breast cancer patients with a defined family history and 760 controls from the Stockholm region. The breast cancer patients originated from; a population-based cohort (n = 452) and from a familial cancer clinic (n = 311), the detailed family history was known in both groups.

Results

The variant was found in 2.9% of the familial cases from the population-based cohort and in 1.9% from the familial cancer clinic. In total 2.2% of the patients with a family history of breast cancer carried the variant compared to 0.7% of the controls (p = 0.03). There was no increased prevalence in sporadic patients (0.3%). The variant was most frequent in young familial patients (5.1% of cases ≤45 years, p = 0.003). The mean age at diagnosis of variant carriers was 12 years lower than in non-carriers (p = 0.001).

Conclusion

In conclusion, CHEK2 1100delC exists in the Swedish population. The prevalence is increased in familial breast cancer and the variant seems to influence age at onset.

Increased Risk of Breast Cancer Associated With CHEK2*1100delC

Purpose

CHEK2*1100delC heterozygosity has been associated with increased risk of breast, prostate, and colorectal cancer in case-control studies. We tested the hypothesis that CHEK2*1100delC heterozygosity in the general population increases the risk of cancer in general, and breast, prostate, and colorectal cancer in particular.

Patients and Methods

We performed a prospective study of 9,231 individuals from the Danish general population, who were observed for 34 years, and we performed a case-control study including 1,101 cases of breast cancer and 4,665 controls.

Results

Of the general population, 0.5% were heterozygotes and 99.5% were noncarriers. In the prospective study, multifactorially adjusted hazard ratios by CHEK2*1100delC heterozygosity versus noncarriers were 1.2 (95% CI, 0.7 to 2.1) for all cancers, 3.2 (95% CI, 1.0 to 9.9) for breast cancer, 2.3 (95% CI, 0.6 to 9.5) for prostate cancer, and 1.6 (95% CI, 0.4 to 6.5) for colorectal cancer. In the case-control study, age-matched odds ratio for breast cancer by CHEK2*1100delC heterozygosity versus noncarriers was 2.6 (95% CI, 1.3 to 5.4). The absolute 10-year risk of breast cancer in CHEK2*1100delC heterozygotes amounted to 24% in women older than 60 years undergoing hormone replacement therapy, with a body mass index of 25 kg/m2 or higher.

Conclusion

CHEK2*1100delC heterozygosity is associated with a three-fold risk of breast cancer in women in the general population.

Breast Cancer Survival and Tumor Characteristics in Premenopausal Women Carrying the CHEK2*1100delC Germline Mutation

Purpose

Women carrying a CHEK2*1100delC germline mutation have an increased risk of developing breast cancer. This study aims to determine the proportion of CHEK2*1100delC carriers in a premenopausal breast cancer population, unselected for family history of breast cancer, and to investigate tumor characteristics and disease outcome with sufficient follow-up.

Patients and Methods

We identified a retrospective cohort of 1,479 patients, who received surgery for invasive breast cancer between 1970 and 1994. All patients were diagnosed before age 50. Paraffin-embedded tissue blocks were collected for DNA isolation (normal tissue), subsequent CHEK2*1100delC analysis, and tumor revision. Median follow-up was 10.1 years.

Results

We detected a CHEK2*1100delC germline mutation in 54 patients (3.7%). Tumor characteristics of CHEK2*1100delC carriers did not differ significantly from those of noncarriers. CHEK2*1100delC carriers had a two-fold increased risk (hazard ratio [HR], 2.1; 95% CI, 1.0 to 4.3; P = .049) of developing a second breast cancer and they had worse recurrence-free survival (HR, 1.7; 95% CI, 1.2 to 2.4; P = .006) and worse breast cancer–specific survival (HR, 1.4; 95% CI, 1.0 to 2.1; P = .072) compared with noncarriers. The poorer disease outcome of CHEK2*1100delC carriers could not be explained by the increased risk of second breast cancer.

Conclusion

Our study, which is representative for the premenopausal breast cancer population, reveals approximately 4% CHEK2*1100delC carriers have an increased risk of second breast cancer and a worse long-term recurrence-free survival rate. Their identification at time of diagnosis and prolonged intensive follow-up should be considered to optimize clinical management.

The breast cancer susceptibility allele CHEK2*1100delC promotes genomic instability in a knock-in mouse model

Allelic variants of CHEK2 contribute to an elevated risk for human breast cancer and possibly other cancer types. In particular, the CHEK2*1100delC polymorphic variant has been identified as a low-penetrance breast cancer susceptibility allele in breast cancer families with wild type BRCA1 and BRCA2. To better understand the molecular basis by which this allele increases risk for disease, we have generated a mouse in which the wild type CHEK2 (Chk2 in mouse) allele has been replaced with the 1100delC variant. Mouse embryo fibroblasts (MEFs) derived from these mice have an altered cell cycle profile in which a far greater proportion of cells are in S-phase and in G2 (4N) compared with wild type cells. The mutant cells show signs of spontaneous genomic instability as indicated by polyploidy and an increase in DNA double strand breaks.

Inherited association of breast and colorectal cancer: limited role of CHEK2 compared with high-penetrance genes

We assessed the association between breast cancer (BC) and colorectal cancer (CRC) from referral pattern to the Regional Genetics Service including molecular analysis. Hospital computer records and/or department referral books were used to identify cases referred to the Regional Genetic Service during a 16-year period (1990-2005 inclusive). All files were reviewed along with associated demographic data, risk assessments, referral details and results from mutation testing. Families were assessed for hereditary breast and colorectal cancer (HBCC) criteria, and all families with eligible individuals were tested for the 1100delC mutation in CHEK2. A total of 8,612 families were identified. One hundred and sixteen of 1,631 (7.5%) families with a primary referral for CRC fulfilled the criteria for HBCC, whereas only 68/6981 (1%) BC referrals fulfilled these criteria. Blood samples were obtained from 113 individuals from 83/184 families. Only 1/113 (1%) has screened positive for the CHEK2 mutation, whereas 14 (17%) families segregate BRCA1/2 mutations and at least 7 (8.5%) carry MLH1/MSH2 mutations. HBCC syndrome, if it exists as a separate entity, is not likely to be due to CHEK2 mutations. Many families are explicable by existing high-penetrance genes, and further work is necessary to elucidate whether the remainder is due to chance or as yet undiscovered genes.

Pathology and gene expression of hereditary breast tumors associated with BRCA1, BRCA2 and CHEK2 gene mutations

Tumors arising in BRCA1 and BRCA2 mutation carriers appear to have specific pathological and gene expression profiles, which show a high level of concordance. BRCA1 tumors are high-grade, negative for hormone receptors, have a high proliferation rate, and are positive for some cell cycle promoter genes. BRCA2 tumors present a phenotype opposite to BRCA1 tumors but very similar to sporadic tumors, except that BRCA2 overexpress some DNA repair markers such as CHEK2, show high cytoplasmic expression of RAD51, and are negative for HER-2 amplification and expression. Some of these characteristics have also been found in cDNA expression studies, although more analysis are necessary in order to obtain new markers that can be associated with a germ line mutation in BRCA1 or BRCA2. In this way, some studies in normal tissues of BRCA1/2 carriers suggest that differences exist in the level of expression of some genes when compared with noncarriers. Finally, IHC studies in tumors carrying a mutation in CHEK2 are rare and show contradictory results, probably due to the low number of these cases. However, they represent an example showing how different mutations of the same gene may be associated with specific histological subtypes of cancer.