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

Introduction Histopathological features of BRCA1 and BRCA2 tumours have previously been characterised and compared with unselected breast tumours; however, familial non-BRCA1/2 tumours are less well known. The aim of this study was to characterise familial non-BRCA1/2 tumours and to evaluate routine immunohistochemical and pathological markers that could help us to further distinguish families carrying BRCA1/2 mutations from other breast cancer families.

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The MRE11, RAD50, and NBS1 genes encode proteins of the MRE11-RAD50-NBS1 (MRN) complex critical for proper maintenance of genomic integrity and tumour suppression; however, the extent and impact of their cancer-predisposing defects, and potential clinical value remain to be determined. Here, we report that among a large series of approximately 1000 breast carcinomas, around 3%, 7% and 10% tumours showed aberrantly reduced protein expression for RAD50, MRE11 and NBS1, respectively. Such defects were more frequent among the ER/PR/ERBB2 triple-negative and higher-grade tumours, among familial (especially BRCA1/BRCA2-associated) rather than sporadic cases, and the NBS1 defects correlated with shorter patients' survival. The BRCA1-associated and ER/PR/ERBB2 triple-negative tumours also showed high incidence of constitutively active DNA damage signalling (gammaH2AX) and p53 aberrations. Sequencing the RAD50, MRE11 and NBS1 genes of 8 patients from non-BRCA1/2 breast cancer families whose tumours showed concomitant reduction/loss of all three MRN-complex proteins revealed two germline mutations in MRE11: a missense mutation R202G and a truncating mutation R633STOP (R633X). Gene transfer and protein analysis of cell culture models with mutant MRE11 implicated various destabilization patterns among the MRN complex proteins including NBS1, the abundance of which was restored by re-expression of wild-type MRE11. We propose that germline mutations qualify MRE11 as a novel candidate breast cancer susceptibility gene in a subset of non-BRCA1/2 families. Our data have implications for the concept of the DNA damage response as an intrinsic anti-cancer barrier, various components of which become inactivated during cancer progression and also represent the bulk of breast cancer susceptibility genes discovered to date.

Cyclin B1 regulates the G 2 -M transition of the cell cycle. Cyclin B1 expression is higher in premalignant and malignant than normal breast lesions. Correlation of cyclin B1 expression with other histopathological variables and prognostic role in breast cancer are not fully understood. Traditionally used prognostic criteria identify large subset of patients to receive adjuvant chemotherapy and to be exposed to adverse effects. A reliable and simple method helping prognostic evaluation in breast cancer is needed. We analysed cyclin B1 expression on 1348 invasive breast cancers and studied correlations with other histopathological variables and survival. High cyclin B1 correlated with high tumour grade, large tumour size and positive nodal status, oestrogen and progesterone receptor negativity, positive HER2 and p53 status, young age at diagnosis, and high cyclin E, cyclin A and Ki67 expression. Among patients not given adjuvant chemotherapy high cyclin B1 was a strong predictor of shorter overall and metastasis-free survival (RR 3.74, Po0.0005 and RR 3.51, Po0.0005, respectively), and remained as an independent prognostic factor also in multivariate analysis (RR 1.80, P ¼ 0.04 and RR 2.31, P ¼ 0.02, respectively). This study suggests high cyclin B1 associates with aggressive phenotype and is an independent prognostic factor in breast cancer.

Mutations in the two breast-ovarian cancer susceptibility genes, BRCA1 and BRCA2, account for a varying fraction of breast cancer families in different populations (Szabo and King, 1997). Both BRCA1 and BRCA2 mutations are scattered throughout the large coding regions of the genes (Breast Cancer Information Core). In admixed populations, most mutations appear uniquely in single families only, making the mutation screening laborious and expensive. Furthermore, there is also evidence of other predisposing genes (Ford et al, 1998;Kainu et al, 2000). It is, therefore, important to find the clinical risk factors that could best predict the presence of BRCA1 and BRCA2 mutations, so that the screening could be directed to potential mutation carrier families. Several probability models for mutation detection have been developed. These are, however, based only on BRCA1 (Berry et al, 1997;Couch et al, 1997;Shattuck-Eidens et al, 1997), focus on specific founder mutations in the Ashkenazi population (Foulkers et al, 1999;Hodgson et al, 1999;Hopper and Jenkins, 1999), or require information such as penetrance estimations not available in all populations (Berry et al, 1997;Parmigiani et al, 1998; ChangClaude et al, 1999).Here we have developed a model for predicting the presence of a BRCA1 or BRCA2 mutation in families with 3 or more relatives affected with breast or ovarian cancer. We also compared this model with those of Shattuck-Eidens et al (1997) and Couch et al (1997) originally designed for BRCA1 only. Additionally, the frequency of BRCA1/2 mutations was studied in 295 families with two affected family members to evaluate the feasibility of genetic screening in families with moderate family history. PATIENTS AND METHODSThe cohort studied consisted of 148 families with 3 or more 1st or 2nd degree relatives affected with breast or ovarian cancer. The families were identified by patient interviews, and full pedigrees were constructed with the confirmation of all genealogy data through the Finnish population registration as well as diagnostic data through hospital records and/or Finnish Cancer Registry as previously described (Vehmanen et al, 1997a,b;Eerola et al, 2000). Additionally, 295 breast cancer cases with one 1st degree relative affected with breast or ovarian cancer and identified in the patient cohorts described in Eerola et al (2000) were also studied. In the following, these are called small families. The family history of these cases was based on information reported by the index patient. All patients participating in the study signed an informed consent before the blood sample for the genetic analysis was taken. This study has been approved by the Ethical Committees of Departments of Obstetrics and Gynaecology, and Oncology, HUCH, and appropriate permissions were obtained from the Ministry of Social Affairs and Health in Finland.The mutations identified by a complete mutation analysis of the whole coding sequences and exon/intron boundaries of the genes in 95 of these families have been previously reported...

Background: BACH1 (BRCA1-associated C-terminal helicase 1; also known as BRCA1-interacting protein 1, BRIP1) is a helicase protein that interacts in vivo with BRCA1, the protein product of one of the major genes for hereditary predisposition to breast cancer. Previously, two BACH1 germ line missense mutations have been identified in early-onset breast cancer patients with and without family history of breast and ovarian cancer.

The genes predisposing to familial breast cancer are largely unknown, but 5 of the 6 known genes are involved in DNA damage repair. RAD50 is part of a highly conserved complex important in recognising, signalling and repairing DNA double‐strand breaks. Recently, a truncating mutation in the RAD50 gene, 687delT, was identified in 2 Finnish breast cancer families. To evaluate the contribution of RAD50 to familial breast cancer, we screened the whole coding region for mutations in 435 UK and 46 Finnish familial breast cancer cases. We identified one truncating mutation, Q350X, in one UK family. We screened a further 544 Finnish familial breast cancer cases and 560 controls for the 687delT mutation, which was present in 3 cases (0.5%) and 1 control (0.2%). Neither Q350X nor 687delT segregated with cancer in the families in which they were identified. Functional analyses suggested that RAD50 687delT is a null allele as there was no detectable expression of the mutant protein. However, the wild‐type allele was retained and expressed in breast tumors from mutation carriers. The abundance of the full‐length RAD50 protein was reduced in carrier lymphoblastoid cells, suggesting a possible haploinsufficiency mechanism. These data indicate that RAD50 mutations are rare in familial breast cancer and either carry no, or a very small, increased risk of cancer. Altogether, these results suggest RAD50 can only be making a very minor contribution to familial breast cancer predisposition in UK and Finland. © 2005 Wiley‐Liss, Inc.