Mechanisms of increased risk of tumorigenesis in Atm and Brca1 double heterozygosity

Multi-locus inherited neoplasia alleles syndromes in cancer: implications for clinical practice

The popularity of multi-gene testing has identified more families with two or more pathogenic variants (PV) in cancer predisposition genes, also known as 'MINAS' (multilocus inherited neoplasia alleles syndromes). They are at risk of suboptimal treatment and management as little on this topic is known. We conducted a systematic review of published MINAS cases within cancer predisposition genes to understand their association with more severe presentations. We analysed 413 MINAS carriers, which included 33 novel cases from the Cancer Genetics Service, National Cancer Centre Singapore. Statistical tests were conducted to assess association between carrier characteristics and the number PV identified. Results suggest that MINAS carriers have more malignancies (31.7% vs 21.5% vs 10.3% %; p < 0.001), a younger median age of first cancer diagnosis (40.0 vs. 44.0 vs. 49.0 years; p < 0.001) and an early onset of cancer (defined as <5% PV-associated cancer risk at age of diagnosis) (24.9% vs 7.7% vs 4.7%; p < 0.001) compared to monoallelic and non-carriers. We also studied the association of clinical characteristics by the dominant or recessive nature of PV harboured, where more dominant-dominant (D-D) carriers reported multiple malignancies (34.0%), compared to dominant-recessive (D-R) (23.9%) and recessive-recessive (R-R) carriers (20%;) (p = 0.051). Our findings suggest that MINAS carriers are prone to more and younger malignancies and the dominant or recessive nature of PV within double carriers can affect clinical presentation. We suggest a framework to guide management based on the dominant or recessive nature of PV within double PV carriers.

A novel BRCA1 splicing variant detected in an early onset triple-negative breast cancer patient additionally carrying a pathogenic variant in ATM: A case report

The widespread adoption of gene panel testing for cancer predisposition is leading to the identification of an increasing number of individuals with clinically relevant allelic variants in two or more genes. The potential combined effect of these variants on cancer risks is mostly unknown, posing a serious problem for genetic counseling in these individuals and their relatives, in whom the variants may segregate singly or in combination. We report a female patient who developed triple-negative high grade carcinoma in the right breast at the age of 36 years. The patient underwent bilateral mastectomy followed by combined immunotherapy and chemotherapy (IMpassion030 clinical trial). Two years later she developed a skin recurrence on the right anterior chest wall. Despite intensive treatment, the patient died at 40-year-old due to disease progression. Gene panel testing of patient's DNA revealed the presence of a protein truncating variant in ATM [c.1672G>T; p.(Gly558Ter)] and of a not previously reported variant in the BRCA1 exon 22 donor splice site [c.5406+6T>C], whose clinical significance was unknown. The analysis of patient's RNA revealed the up-regulation of two alternative BRCA1 mRNA isoforms derived from skipping of exon 22 and of exons 22-23. The corresponding predicted protein products, p.(Asp1778GlyfsTer27) and p.(Asp1778_His1822del) are both expected to affect the BRCA1 C Terminus (BRCT) domain. The two variants were observed to co-occur also in the proband's brother who, in addition, was heterozygous for a common variant (c.4837A>G) mapped to BRCA1 exon 16. This allowed to ascertain, by transcript-specific amplification, the lack of functional mRNA isoforms expressed by the c.5406+6T>C allele and provided evidence to classify the BRCA1 variant as pathogenic, according to the guidelines of the Evidence-based Network for the Interpretation of Germline Mutant Alleles (ENIGMA) consortium. To our knowledge, excluding two cases detected following the screening of population specific recurrent variants, only one ATM/BRCA1 double heterozygote has been reported in the literature, being the case here described the one with the youngest age at cancer onset. The systematic collection of cases with pathogenic variants in more than one cancer predisposition gene is needed to verify if they deserve ad hoc counseling and clinical management.

Adverse outcome pathways for ionizing radiation and breast cancer involve direct and indirect DNA damage, oxidative stress, inflammation, genomic instability, and interaction with hormonal regulation of the breast

Knowledge about established breast carcinogens can support improved and modernized toxicological testing methods by identifying key mechanistic events. Ionizing radiation (IR) increases the risk of breast cancer, especially for women and for exposure at younger ages, and evidence overall supports a linear dose-response relationship. We used the Adverse Outcome Pathway (AOP) framework to outline and evaluate the evidence linking ionizing radiation with breast cancer from molecular initiating events to the adverse outcome through intermediate key events, creating a qualitative AOP. We identified key events based on review articles, searched PubMed for recent literature on key events and IR, and identified additional papers using references. We manually curated publications and evaluated data quality. Ionizing radiation directly and indirectly causes DNA damage and increases production of reactive oxygen and nitrogen species (RONS). RONS lead to DNA damage and epigenetic changes leading to mutations and genomic instability (GI). Proliferation amplifies the effects of DNA damage and mutations leading to the AO of breast cancer. Separately, RONS and DNA damage also increase inflammation. Inflammation contributes to direct and indirect effects (effects in cells not directly reached by IR) via positive feedback to RONS and DNA damage, and separately increases proliferation and breast cancer through pro-carcinogenic effects on cells and tissue. For example, gene expression changes alter inflammatory mediators, resulting in improved survival and growth of cancer cells and a more hospitable tissue environment. All of these events overlap at multiple points with events characteristic of "background" induction of breast carcinogenesis, including hormone-responsive proliferation, oxidative activity, and DNA damage. These overlaps make the breast particularly susceptible to ionizing radiation and reinforce that these biological activities are important characteristics of carcinogens. Agents that increase these biological processes should be considered potential breast carcinogens, and predictive methods are needed to identify chemicals that increase these processes. Techniques are available to measure RONS, DNA damage and mutation, cell proliferation, and some inflammatory proteins or processes. Improved assays are needed to measure GI and chronic inflammation, as well as the interaction with hormonally driven development and proliferation. Several methods measure diverse epigenetic changes, but it is not clear which changes are relevant to breast cancer. In addition, most toxicological assays are not conducted in mammary tissue, and so it is a priority to evaluate if results from other tissues are generalizable to breast, or to conduct assays in breast tissue. Developing and applying these assays to identify exposures of concern will facilitate efforts to reduce subsequent breast cancer risk.

Adverse outcome pathways for ionizing radiation and breast cancer involve direct and indirect DNA damage, oxidative stress, inflammation, genomic instability, and interaction with hormonal regulation of the breast

Knowledge about established breast carcinogens can support improved and modernized toxicological testing methods by identifying key mechanistic events. Ionizing radiation (IR) increases the risk of breast cancer, especially for women and for exposure at younger ages, and evidence overall supports a linear dose-response relationship. We used the Adverse Outcome Pathway (AOP) framework to outline and evaluate the evidence linking ionizing radiation with breast cancer from molecular initiating events to the adverse outcome through intermediate key events, creating a qualitative AOP. We identified key events based on review articles, searched PubMed for recent literature on key events and IR, and identified additional papers using references. We manually curated publications and evaluated data quality. Ionizing radiation directly and indirectly causes DNA damage and increases production of reactive oxygen and nitrogen species (RONS). RONS lead to DNA damage and epigenetic changes leading to mutations and genomic instability (GI). Proliferation amplifies the effects of DNA damage and mutations leading to the AO of breast cancer. Separately, RONS and DNA damage also increase inflammation. Inflammation contributes to direct and indirect effects (effects in cells not directly reached by IR) via positive feedback to RONS and DNA damage, and separately increases proliferation and breast cancer through pro-carcinogenic effects on cells and tissue. For example, gene expression changes alter inflammatory mediators, resulting in improved survival and growth of cancer cells and a more hospitable tissue environment. All of these events overlap at multiple points with events characteristic of "background" induction of breast carcinogenesis, including hormone-responsive proliferation, oxidative activity, and DNA damage. These overlaps make the breast particularly susceptible to ionizing radiation and reinforce that these biological activities are important characteristics of carcinogens. Agents that increase these biological processes should be considered potential breast carcinogens, and predictive methods are needed to identify chemicals that increase these processes. Techniques are available to measure RONS, DNA damage and mutation, cell proliferation, and some inflammatory proteins or processes. Improved assays are needed to measure GI and chronic inflammation, as well as the interaction with hormonally driven development and proliferation. Several methods measure diverse epigenetic changes, but it is not clear which changes are relevant to breast cancer. In addition, most toxicological assays are not conducted in mammary tissue, and so it is a priority to evaluate if results from other tissues are generalizable to breast, or to conduct assays in breast tissue. Developing and applying these assays to identify exposures of concern will facilitate efforts to reduce subsequent breast cancer risk.

Double heterozygous mutation in the BRCA1 and ATM genes involved in development of primary metachronous tumours: a case report

PURPOSE

Between 5 and 10% of cases of breast cancer (BC) are attributable to a genetic susceptibility. The BRCA1 and BRCA2 genes described in the late 1990s are associated with an increased risk of breast and ovarian cancer, and the clinical management of carriers of pathogenic variants in these genes is defined in several clinical guidelines (Paluch-Shimon et al. in Ann Oncol 27(suppl 5):v103-v110, 2016; Llort et al. in Clin Transl Oncol 17(12):956-961, 2015). However, the pathogenic variants in BRCA1 and BRCA2 represent only a third of the causes of hereditary BC (Easton et al. in N Engl J Med 372:2243-2257, 2015). The incorporation of NGS (Next Generation Sequencing) techniques in the genetic diagnosis of this pathology, in addition to minimising the cost and time of analysis, allows the simultaneous study of other genes of high and moderate penetrance (Easton et al. in N Engl J Med 372:2243-2257, 2015; Op. Cit.; Tung et al. in Cancer 121(1):25-33, 2015). To date, there are not many cases or series of patients that describe the co-occurrence of two pathogenic variants in these genes of BC. Cases of double heterozygosis have been described with the presence of pathogenic variants in BRCA1, BRCA2, PALB2, CHEK2, BLM or NBN (Nomizu et al. in Breast Cancer 22(5):557-61, 2015; Heidemann et al. in Breast Cancer Res Treat 134(3):1229-1239, 2012; Zuradelli et al. in Breast Cancer Res Treat 124(1):251-258, 2010; Sokolenko et al. in Breast Cancer Res Treat 145(2):553-562, 2014).

METHODS

We report the case of a patient diagnosed with multiple tumours who presented two pathogenic variants in heterozygosis.

RESULTS

Two pathogenic variants, c.5123C > A (p.Ala1708Glu) in the BRCA1 gene and c.2413C > T (p.Arg805X) in the ATM gene were detected in heterozygosis. Said variants were confirmed by Sanger-type sequencing using specific primers.

CONCLUSIONS

The implementation of gene panels using NGS in the study of hereditary cancer involves the detection of heterozygous double mutations in genes of high and moderate penetrance for cancer, although with a low frequency.