Breast cancer and radiotherapy in ataxia-telangiectasia heterozygote

Ataxia-telangiectasia gene (ATM) mutation heterozygosity in breast cancer: a narrative review

Background

Despite the fact that heterozygosity for a pathogenic ATM variant is present in 1%-2% of the adult population, clinical guidelines to inform physicians and genetic counsellors about optimal management in that population are lacking.

Methods

In this narrative review, we describe the challenges and controversies in the management of women who are heterozygous for a pathogenic ATM variant with respect to screening for breast and other malignancies, to choices for systemic therapy, and to decisions about radiation therapy.

Results

Given that the lifetime risk for breast cancer in women who are heterozygous for a pathogenic ATM variant is likely greater than 25%, those women should undergo annual mammographic screening starting at least by 40 years of age. For women in this group who have a strong family history of breast cancer, earlier screening with both magnetic resonance imaging and mammography should be considered. High-quality data to inform the management of established breast cancer in carriers of pathogenic ATM variants are lacking. Although deficiency in the ATM gene product might confer sensitivity to dna-damaging pharmaceuticals such as inhibitors of poly (adp-ribose) polymerase or platinum agents, prospective clinical trials have not been conducted in the relevant patient population. Furthermore, the evidence with respect to radiation therapy is mixed; some data suggest increased toxicity, and other data suggest improved clinical benefit from radiation in women who are carriers of a pathogenic ATM variant.

Conclusions

As in the 2017 U.S. National Comprehensive Cancer Network guidelines, we recommend high-risk imaging for women in Ontario who are heterozygous for a pathogenic ATM variant. Currently, ATM carrier status should not influence decisions about systemic or radiation therapy in the setting of an established breast cancer diagnosis.

ATM gene mutations in sporadic breast cancer patients from Brazil

Purpose

The Ataxia-telangiectasia mutated (ATM) gene encodes a multifunctional kinase, which is linked to important cellular functions. Women heterozygous for ATM mutations have an estimated relative risk of developing breast cancer of 3.8. However, the pattern of ATM mutations and their role in breast cancer etiology has been controversial and remains unclear. In the present study, we investigated the frequency and spectrum of ATM mutations in a series of sporadic breast cancers and controls from the Brazilian population.

Methods

Using PCR-Single Strand Conformation Polymorphism (SSCP) analysis and direct DNA sequencing, we screened a panel of 100 consecutive, unselected sporadic breast tumors and 100 matched controls for all 62 coding exons and flanking introns of the ATM gene.

Results

Several polymorphisms were detected in 12 of the 62 coding exons of the ATM gene. These polymorphisms were observed in both breast cancer patients and the control population. In addition, evidence of potential ATM mutations was observed in 7 of the 100 breast cancer cases analyzed. These potential mutations included six missense variants found in exon 13 (p.L546V), exon 14 (p.P604S), exon 20 (p.T935R), exon 42 (p.G2023R), exon 49 (p.L2307F), and exon 50 (p.L2332P) and one nonsense mutation in exon 39 (p.R1882X), which was predicted to generate a truncated protein.

Conclusions

Our results corroborate the hypothesis that sporadic breast tumors may occur in carriers of low penetrance ATM mutant alleles and these mutations confer different levels of breast cancer risk.

Electronic supplementary material

The online version of this article (doi:10.1186/s40064-015-0787-z) contains supplementary material, which is available to authorized users.

FGFR2 genotype and risk of radiation-associated breast cancer in Hodgkin lymphoma

Women treated at young ages with supradiaphragmatic radiotherapy for Hodgkin lymphoma (HL) have a highly increased risk of breast cancer. For personalized advice and follow-up regimens for patients, information is needed on how the radiotherapy-related risk is affected by other breast cancer risk factors. Genome-wide association studies have identified 14 independently replicated common single nucleotide polymorphisms that influence breast cancer risk. To examine whether these variants contribute to risk of radiation-associated breast cancer in HL, we analyzed 2 independent case-control series, from the United Kingdom and The Netherlands, totaling 693 HL patients, 232 with breast cancer and 461 without. rs1219648, which annotates the FGFR2 gene, was associated with risk in both series (combined per-allele odds ratio = 1.59, 95% confidence interval: 1.26-2.02; P = .000111). These data provide evidence that genetic variation in FGFR2 influences radiation-induced breast cancer risk.

Clinical radiosensitivity in breast cancer patients carrying pathogenic ATM gene mutations: no observation of increased radiation-induced acute or late effects

BACKGROUND AND PURPOSE

Reports on increased late subcutaneous toxicity after radiation therapy (RT) in breast cancer patients carrying ATM gene mutations has raised concerns about RT as part of the management in these patients. The impact of ataxia-telangiectasia (A-T) heterozygosity on clinical radiosensitivity remains a matter of debate while clinical data are scarce.

PATIENTS AND METHODS

Between September 1995 and December 2002 genomic DNA samples were collected from 1100 unselected breast cancer patients receiving adjuvant radiotherapy at our department. Using mutation-specific assays, we screened for frequent ATM gene mutations. Analysis of acute and late radiation-related toxicity for skin and subcutaneous normal tissue was performed in patients identified as A-T heterozygotes applying common toxicity criteria (CTC) and LENT/SOMA (late effects on normal tissue/subjective objective management analytic) scoring criteria, respectively.

RESULTS

Eleven patients were identified to be heterozygous for a pathogenic ATM gene mutation. Ten patients had received at least one course of RT. Median follow-up after completion of radiotherapy was 5.1 years (range 1.7-7.2). There was no evidence of increased radiation-induced acute or late skin or subcutaneous reactions in patients treated with linac-based RT. One patient failed distantly and was subsequently irradiated at four different sites for bone and brain metastases. Local relapse occurred in the single patient who had declined adjuvant RT following breast conservative therapy.

CONCLUSIONS

Our results do not provide evidence for a relative contraindication to adjuvant RT in A-T heterozygous breast cancer patients. Due to their increased cellular radiosensitivity, these patients may differentially benefit from RT and qualify for dose and volume reduction trials.

Second primary breast cancer after Hodgkin's disease

Although the potential carcinogenic risk of radiotherapy is well known, it has become clear that there is a particularly high risk of radiation-induced breast cancer in women treated for Hodgkin's disease at young ages. Thankfully, death from breast cancer in this population is uncommon, but it is important to understand factors contributing to the risk, including treatment parameters, and to develop a logical and efficient method for medical management of those at risk. In this minireview, we examine the evidence which should inform such a management policy.

Screening women at high risk of breast cancer on the basis of evidence

Geneticists are able to identify the risk of breast cancer. Strategies on offer include prevention, early diagnosis by screening, and prophylactic surgery. This paper analyses the evidence for offering screening. The radiation dose of mammography has been measured, but the risk is not fully known. Mammography screening of women of 40-50 years in the normal population has known effect. Little evidence is available for women under 40 years or for women with genetic susceptibility to breast cancer. Dense parenchymal pattern is associated with high grade cancers, and is both a risk factor and a reason for impaired screening sensitivity. Whether this applies to younger women or women at high risk is speculative. The pathological features of the cancers in gene carriers show differences from those occurring in normal women. This work should be correlated with imaging features. There is no literature to support the use of newer imaging methods in these women. Ultrasound and MRI avoid radiation and may be useful in dense breasts. SestaMIBI and PET scanning are not yet mature enough for screening, and may never have such a role. Any newer modality must be subjected to a formal randomised trial before being offered to screen women at high risk.

Postmastectomy radiotherapy: clinical practice guidelines of the American Society of Clinical Oncology

OBJECTIVE

To determine indications for the use of postmastectomy radiotherapy (PMRT) for patients with invasive breast cancer with involved axillary lymph nodes or locally advanced disease who receive systemic therapy. These guidelines are intended for use in the care of patients outside of clinical trials.

POTENTIAL INTERVENTION

The benefits and risks of PMRT in such patients, as well as subgroups of these patients, were considered. The details of the PMRT technique were also evaluated.

OUTCOMES

The outcomes considered included freedom from local-regional recurrence, survival (disease-free and overall), and long-term toxicity.

EVIDENCE

An expert multidisciplinary panel reviewed pertinent information from the published literature through July 2000; certain investigators were contacted for more recent and, in some cases, unpublished information. A computerized search was performed of MEDLINE data; directed searches based on the bibliographies of primary articles were also performed.

VALUES

Levels of evidence and guideline grades were assigned by the Panel using standard criteria. A "recommendation" was made when level I or II evidence was available and there was consensus as to its meaning. A "suggestion" was made based on level III, IV, or V evidence and there was consensus as to its meaning. Areas of clinical importance were pointed out where guidelines could not be formulated due to insufficient evidence or lack of consensus.

RECOMMENDATIONS

The recommendations, suggestions, and expert opinions of the Panel are described in this article.

VALIDATION

Seven outside reviewers, the American Society of Clinical Oncology (ASCO) Health Services Research Committee members, and the ASCO Board of Directors reviewed this document.

Increased risk of breast cancer following irradiation for Hodgkin's disease is not a result of ATM germline mutations

PURPOSE

Long-term survivors of Hodgkin's disease who received mantle-field irradiation at a young age have a strongly increased risk of developing breast cancer. The purpose of this study was to investigate whether this increased risk was substantially greater among women heterozygous for a germline mutation in the ataxia-telangiectasia gene (ATM).

MATERIALS AND METHODS

Thirty-two patients were selected who had developed breast cancer at least 10 years following irradiation for Hodgkin's disease before the age of 45 years. In these patients, the complete open reading frame of the ATM gene was analysed for the presence of germline mutations using the protein truncation test and two mutation-specific tests, followed by genomic sequencing.

RESULTS

No A-T disease causing germline mutations were found in these selected Hodgkin patients. However, several alternative splicing events were detected which might influence protein expression levels.

CONCLUSIONS

The data suggest that truncating mutations in the ATM gene are not a major component underlying the increased risk of breast cancer following Hodgkin's disease.

The ATM gene and breast cancer: is it really a risk factor?

The genetic determinants for most breast cancer cases remain elusive. Whilst mutations in BRCA1 and BRCA2 significantly contribute to familial breast cancer risk, their contribution to sporadic breast cancer is low. In such cases genes frequently altered in the general population, such as the gene mutated in Ataxia telangiectasia (AT), ATM may be important risk factors. The initial interest in studying ATM heterozygosity in breast cancer arose from the findings of epidemiological studies of AT families in which AT heterozygote women had an increased risk of breast cancer and estimations that 1% of the population are AT heterozygotes. One of the clinical features of AT patients is extreme cellular sensitivity to ionising radiation. This observation, together with the finding that a significant proportion of breast cancer patients show an exaggerated acute or late normal tissue reactions after radiotherapy, has lead to the suggestion that AT heterozygosity plays a role in radiosensitivity and breast cancer development. Loss of heterozygosity in the region of the ATM gene on chromosome 11, has been found in about 40% of sporadic breast tumours. However, screening for ATM mutations in sporadic breast cancer cases, showing or not adverse effects to radiotherapy, has not revealed the magnitude of involvement of the ATM gene expected. Their size and the use of the protein truncation test to identify mutations limit many of these studies. This latter parameter is critical as the profile of mutations in AT patients may not be representative of the ATM mutations in other diseases. The potential role of rare sequence variants within the ATM gene, sometimes reported as polymorphisms, also needs to be fully assessed in larger cohorts of breast cancer patients and controls in order to determine whether they represent cancer and/or radiation sensitivity predisposing mutations.

Enhanced radiation late effects and cellular radiation sensitivity in an ATM heterozygous breast cancer patient

We observed severe late effects in a patient treated with radiation therapy for breast cancer. Radiation survival studies of patient fibroblasts show an enhanced cellular radiation sensitivity (Do = 0.95 Gy). Genetic analysis reveals that the patient is heterozygous for a mutated ATM gene. Protein truncation test (PTT) and sequence analysis identified a truncation within the leucine zipper domain, corresponding to a fragment previously reported to exhibit dominant negative function. These findings demonstrate that ATM heterozygosity may be associated with enhanced clinical radiation sensitivity and suggest a clinical relevance to this truncation that results in a dominant negative-acting protein.

Sequence analysis of the ATM gene in 20 patients with RTOG grade 3 or 4 acute and/or late tissue radiation side effects

PURPOSE

Patients with ataxia-telangiectasia (A-T) show greatly increased radiation sensitivity and cancer predisposition. Family studies imply that the otherwise clinically silent heterozygotes of this autosomal recessive disease run a 3.5 to 3.8 higher risk of developing cancer. In vitro studies suggest moderately increased cellular radiation sensitivity of A-T carriers. They may also show elevated clinical radiosensitivity. We retrospectively examined patients who presented with severe adverse reactions during or after standard radiation treatment for mutations in the gene responsible for A-T, ATM, considering a potential means of future identification of radiosensitive individuals prospectively to adjust dosage schedules.

MATERIAL AND METHODS

We selected 20 cancer patients (breast, 11; rectum, 2; ENT, 2; bladder, 1; prostate, 1; anus, 1; astrocytoma, 1; Hodgkins lymphoma, 1) with Grade 3 to 4 (RTOG) acute and/or late tissue radiation side effects by reaction severity. DNA from the peripheral blood of patients was isolated. All 66 exons and adjacent intron regions of the ATM gene were PCR-amplified and examined for mutations by a combination of agarose gel electrophoresis, single-stranded conformational polymorphism (SSCP) analysis, and exon-scanning direct sequencing.

RESULTS

Only 2 of the patients revealed altogether four heteroallelic sequence variants. The latter included two single-base deletions in different introns, a single-base change causing an amino acid substitution in an exon, and a large insertion in another intron. Both the single-base deletions and the single-base change represent known polymorphisms. The large insertion was an Alu repeat, shown not to give rise to altered gene product.

CONCLUSIONS

Despite high technical efforts, no unequivocal ATM mutation was detected. Nevertheless, extension of similar studies to larger and differently composed cohorts of patients suffering severe adverse effects of radiotherapy, and application of new technologies for mutation detection may be worthwhile to assess the definite prevalence of significant ATM mutations within the group of radiotherapy patients with adverse reactions. To date, it must be recognized that our present results do not suggest that heterozygous ATM mutations are involved in clinically observed radiosensitivity but, rather, invoke different genetic predisposition or so far unknown exogenous factors.

Radiation, DNA damage and cancer

The characterization of the rare, radiation-sensitive and cancer-prone syndromes, ataxia telangiectasia and Nijmegen breakage syndrome, has demonstrated that genetic predisposition increases the risk of developing cancer after exposure to ionizing radiation (IR). Molecular analyses of these disorders provide valuable insights into the normal function of these two gene products in the cellular response to IR-induced DNA damage. Their contribution to a cellular radiosensitive phenotype and their role in sporadic cancers can now be fully assessed. For example, the gene ataxia telangiectasia mutated (ATM) has recently been shown to be a tumour suppressor gene in T-cell prolymphocytic leukaemia, and there is increasing evidence that individuals with one mutated ATM or Nijmegen breakage syndrome (NBS1) allele have an increased predisposition to cancer.

Cellular responses to radiation and risk of breast cancer

Mutations in the ataxia telangiectasia gene (ATM) result in an abnormal p53-mediated cellular response to DNA damage produced by ionising radiation. This deficiency is believed to contribute to the radiosensitivity and high cancer risk seen in ataxia telangiectasia (AT) patients and AT heterozygotes. Epidemiological studies have demonstrated that relatives of AT patients are particularly predisposed to breast cancer. This observation, together with the finding that a relatively high proportion of breast cancer patients display an abnormal severe reaction of normal tissues following radiotherapy, has led to the suggestion that AT heterozygosity plays a role in radiosensitivity and breast cancer development. The cloning of the ATM gene has allowed this possibility to be examined at the molecular level. The studies reported to date remain inconclusive, with the number of AT heterozygotes being found in radiosensitive breast cancer patients being less than would be expected based on the family studies. The potential role of several other recently identified genes which are involved in the cellular DNA damage response to ionising radiation and which could also play a role in radiosensitivity and breast cancer development are reviewed.

Radiosensitivity of normal tissues in ataxia-telangiectasia heterozygotes

PURPOSE

Approximately 5% of cancer patients given radiation therapy exhibit severe injuries to the noncancerous tissue in the radiation field. Striking clinical sensitivity to ionizing radiation has been observed frequently in ataxia-telangiectasia (A-T) homozygotes. This study was undertaken to test the hypothesis that heterozygous carriers of a mutated gene for A-T may represent a substantial proportion of all patients who suffer severe radiation toxicity.

METHODS

The medical records of all A-T heterozygotes treated with radiation therapy for breast or prostate cancer were compiled from an ongoing study of mortality and cancer incidence in A-T families. Diagnostic, treatment, and follow-up records were reviewed. Acute and long-term radiation complications were scored according to Radiation Therapy and Oncology Group criteria.

RESULTS

There were no instances of soft tissue necrosis or other apparent serious injuries to normal tissues of two A-T heterozygotes with prostate carcinoma and 11 with breast carcinoma who received moderate-to-high doses of conventionally fractionated radiation therapy by megavoltage techniques.

CONCLUSION

There is no evidence that abnormal clinical radiosensitivity occurs in A-T heterozygotes receiving conventionally fractionated radiation therapy for breast or prostate cancer.

Heterozygosity for mutations in the ataxia telangiectasia gene is not a major cause of radiotherapy complications in breast cancer patients

Of patients being treated by radiotherapy for cancer, a small proportion develop marked long-term radiation damage. It is believed that this is due, at least in part, to intrinsic individual differences in radiosensitivity, but the underlying mechanism is unknown. Individuals affected by the recessive disease ataxia telangiectasia (AT) exhibit extreme sensitivity to ionizing radiation. Cells from such individuals are also radiosensitive in in vitro assays, and cells from AT heterozygotes are reported to show in vitro radiosensitivity at an intermediate level between homozygotes and control subjects. In order to examine the possibility that a defect in the ATM gene may account for a proportion of radiotherapy complications, 41 breast cancer patients developing marked changes in breast appearance after radiotherapy and 39 control subjects who showed no clinically detectable reaction after radiotherapy were screened for mutations in the ATM gene. One out of 41 cases showing adverse reactions was heterozygous for a mutation (insertion A at NT 898) that is predicted to generate a truncated protein of 251 amino acids. No truncating mutations were detected in the control subjects. On the basis of this result, the estimated percentage (95% confidence interval) of AT heterozygous patients in radiosensitive cases was 2.4% (0.1-12.9%) and in control subjects (0-9.0%). We conclude that ATM gene defects are not the major cause of radiotherapy complications in women with breast cancer.

Testing for mutations of the ataxia telangiectasia gene in radiosensitive breast cancer patients

BACKGROUND AND PURPOSE

To determine if clinical radiosensitivity in breast cancer patients is related to mutations of the ataxia telangiectasia gene (ATM).

MATERIALS AND METHODS

Fifteen patients who had developed a severe late reaction to a standard radiotherapy schedule were examined for evidence of increased in vitro radiosensitivity using the MTT assay. Mutation analysis was performed using a protein truncation assay.

RESULTS

No mutations were detected in the 15 patients despite evidence of increased in vitro radiosensitivity.

CONCLUSIONS

Testing for the ATM gene is unlikely to be useful for predicting clinical response to radiotherapy in breast cancer patients.

Heterozygous ATM mutations do not contribute to early onset of breast cancer

Ataxia telangiectasia (AT) is a recessive syndrome, including cerebellar degeneration, immunologic defects and cancer predisposition, attributed to mutations in the recently isolated ATM (ataxia telangiectasia, mutated) gene. AT is diagnosed in 1/40,000 to 1/100,000 live births, with carriers calculated to comprise approximately 1% of the population. Studies of AT families have suggested that female relatives presumed to be carriers have a 5 to 8-fold increased risk for developing breast cancer, raising the possibility that germline ATM mutations may account for approximately 5% of all breast cancer cases. The increased risk for breast cancer reported for AT family members has been most evident among younger women, leading to an age-specific relative risk model predicting that 8% of breast cancer in women under age 40 arises in AT carriers, compared with 2% of cases between 40-59 years. To test this hypothesis, we undertook a germ-line mutational analysis of the ATM gene in a population of women with early onset of breast cancer, using a protein truncation (PTT) assay to detect chain-terminating mutations, which account for 90% of mutations identified in children with AT. We detected a heterozygous ATM mutation in 2/202 (1%) controls, consistent with the frequency of AT carriers predicted from epidemiologic studies. ATM mutations were present in only 2/401 (0.5%) women with early onset of breast cancer (P = 0.6). We conclude that heterozygous ATM mutations do not confer genetic predisposition to early onset of breast cancer.

Absence of mutations in the ATM gene in breast cancer patients with severe responses to radiotherapy

The effectiveness of cancer radiotherapy is compromised by the small proportion (approximately 5%) of patients who sustain severe normal tissue damage after standard radiotherapy treatments. Predictive tests are required to identify these highly radiosensitive cases. Patients with the rare, recessively inherited, cancer-prone syndrome ataxia-telangiectasia (A-T) sustain extremely severe normal tissue necrosis after radiotherapy and their cultured cells are also highly radiosensitive. Clinically normal carriers (heterozygotes) of the A-T gene have an increased risk of breast cancer, account for approximately 4% of all breast cancer cases and show a modest increase in cellular radiosensitivity in vitro. It has been suggested that a substantial proportion of highly radiosensitive (HR) breast cancer patients may be A-T heterozygotes, and that screening for mutations in the A-T gene could be used as a predictive test. We have tested this hypothesis in a group of cancer patients who showed adverse reactions to radiotherapy. Sixteen HR breast cancer patients showing mainly acute reactions (and seven HR patients with other cancers) were tested for ATM mutations using the restriction endonuclease fingerprinting assay. No mutations typical of those found in obligate A-T heterozygotes were detected. If the estimate that 4% of breast cancer cases are A-T gene carriers is correct, then ATM mutations do not confer clinical radiosensitivity. These early results suggest that screening for ATM mutations in cancer patients may not be of value in predicting adverse reactions.