Asymptomatic Bloom syndrome diagnosed by chance in a patient with breast cancer

Bloom syndrome (BS) is a rare genetic disorder caused by biallelic inactivation of the BLM gene, which usually manifests in childhood by significant growth retardation, immune deficiency, characteristic skin lesions, cancer predisposition and other distinguishable disease features. To our knowledge, all prior instances of BS have been identified via intentional analysis of patients with clinical suspicion for this disease or DNA testing of members of affected pedigrees. We describe an incidental finding of BS, which occurred upon routine germline DNA analysis of consecutive breast cancer patients. The person with the biallelic pathogenic BLM c.1642C>T (p.Gln548Ter) variant remained clinically healthy for 38 years until she developed breast cancer. Detailed examination of this woman, which was carried out after the genetic diagnosis, revealed mild features of BS. A sister chromatid exchange (SCE) test confirmed the presence of this syndrome. The tumor exhibited triple-negative receptor status, a high proliferation rate, a low tumor mutation burden (TMB), and a moderate level of chromosomal instability (homologous recombination deficiency (HRD) score = 29). The patient showed normal tolerability to radiotherapy and several regimens of cytotoxic therapy. Thus, some BS patients may remain undiagnosed due to the mild phenotype of their disease. BLM should be incorporated in gene panels utilized for germline DNA testing of cancer patients.

Sister chromatid exchange assay as a predictor of tumor chemoresponse

Sister Chromatid Exchanges (SCEs) are known to enhance as a consequence of exposure to various mutagenic agents and appear to indicate DNA damaging effects and/or subsequent repair by homologous recombination (HR). DNA damage plays an interesting role in the majority of mechanisms underlying the effects of antitumor drugs, since the genetic activity of the plethora of these agents is due to their ability to damage the DNA. The DNA-effects of antitumor agents towards normal cells (genotoxicity) are great drawbacks of antitumor therapy and are connected to important adverse health effects in cancer patients undergoing chemotherapy. On the other hand, failure of chemotherapy in many cases is due to the DNA repair ability which cancer, like normal cells, also possess. As both DNA repair and genotoxic exposure are expected to vary among patients, correlating SCEs frequencies with only individual repair capacity may be feasible to predict. Cancer risk has not been observed to be associated with high SCEs levels. Since the administration of effective antitumor drugs with limited adverse effects is of great importance in the success of anticancer therapy, a lot of interest has been directed toward the development of methods and approaches that would enable the correct selection of appropriate drugs prior to the initiation of therapy on an individual basis. To this effect, more than 30 years ago, an investigation of the ability of the in vitro and the in vivo SCEs-assay to predict the in vitro and in vivo sensitivity of tumor cells to newly synthesized drugs or to those already in use began. In this short review a critical appraisal of the SCEs-assay as an important biomarker used for predicting cancer chemo-response as well as a summary of the key findings from several studies published within the last 20 years in this field is performed.

Sister chromatid exchange: A possible approach to characterize familial breast cancer patients

Sister chromatid exchange (SCE) frequency is widely used as an indicator of spontaneous chromosome instability. We investigated SCE frequency in the peripheral blood lymphocytes of familial and sporadic breast cancer (BC) patients from the Apulian Caucasian Population. Eighty-one patients were enrolled: 22 with familial history and 59 sporadic patients. Eleven familial patients had an 'increased risk' of BRCA gene mutation (BRCAPro ≥ 10%) and were candidates for BRCA1 and BRCA2 mutation analysis. For these reasons, we stratified the 22 familial BC patients in two group: 'low-risk' (n=11) and 'high-risk' (n=11) patients for BRCA gene mutations. Two of these 11 'high-risk' patients (18%) had pathogenic mutations in the BRCA2 gene. The subjects were not cigarette smokers or alcohol or drug users, and had no genetic disorders or chronic diseases affecting the family. Our results showed a significant increase in SCE frequency in the familial (5.305 ± 1.088/metaphase) (P<0.0001) and the sporadic patients (3.943 ± 0.552) (P<0.0001) compared to the controls (3.197 ± 0.649). We found that the SCE frequency was always significantly higher in familial than in sporadic patients, regardless of their clinicopathological characteristics. Moreover, we observed that the frequency of SCE in BRCA2 mutation carrier patients was higher compared to patients without mutations in BRCA1/2 genes. These findings highlight an intrinsic genomic instability in familial patients, and we suggest that SCE frequency may be used as a biomarker to better characterize familial BC.

Evidence that BRCA1- or BRCA2-associated cancers are not inevitable

Inheriting a BRCA1 or BRCA2 gene mutation can cause a deficiency in repairing complex DNA damage. This step leads to genomic instability and probably contributes to an inherited predisposition to breast and ovarian cancer. Complex DNA damage has been viewed as an integral part of DNA replication before cell division. It causes temporary replication blocks, replication fork collapse, chromosome breaks and sister chromatid exchanges (SCEs). Chemical modification of DNA may also occur spontaneously as a byproduct of normal processes. Pathways containing BRCA1 and BRCA2 gene products are essential to repair spontaneous complex DNA damage or to carry out SCEs if repair is not possible. This scenario creates a theoretical limit that effectively means there are spontaneous BRCA1/2-associated cancers that cannot be prevented or delayed. However, much evidence for high rates of spontaneous DNA mutation is based on measuring SCEs by using bromodeoxyuridine (BrdU). Here we find that the routine use of BrdU has probably led to overestimating spontaneous DNA damage and SCEs because BrdU is itself a mutagen. Evidence based on spontaneous chromosome abnormalities and epidemiologic data indicates strong effects from exogenous mutagens and does not support the inevitability of cancer in all BRCA1/2 mutation carriers. We therefore remove a theoretical argument that has limited efforts to develop chemoprevention strategies to delay or prevent cancers in BRCA1/2 mutation carriers.