Elsevier

Oral Oncology

Volume 48, Issue 8, August 2012, Pages 698-702
Oral Oncology

Correlation of Ataxia-Telangiectasia-Mutated (ATM) gene loss with outcome in head and neck squamous cell carcinoma

https://doi.org/10.1016/j.oraloncology.2012.02.014Get rights and content

Summary

Objectives

Ataxia-Telangiectasia-Mutated (ATM) gene loss has been associated with poor prognosis and treatment resistance in head and neck squamous cell carcinomas (HNSCC). We investigated the relationship between ATM loss detected by fluorescence in-situ hybridisation (FISH) with patient outcome, and its relationship with Human Papillomavirus (HPV)/p16INK4A status.

Material and methods

Copy number of the ATM gene and chromosome 11 were determined by FISH and HPV status was determined using p16INK4A immunohistochemistry in 87 paraffin embedded tumour samples from patients with HNSCC treated with chemoradiation at a single institution. ATM loss was correlated with patient outcome as both a continuous and dichotomous variable.

Results

Of 73 evaluable patients, 44 (60.3%) demonstrated loss of the ATM gene. There was no correlation between ATM loss (defined as a mean ratio of ATM: chromosome 11 < 0.75) and overall survival (OS, p = 0.67) or time to locoregional failure (TTLRF, p = 0.72). Similarly, when evaluated as a continuous variable there was no significant relationship between ATM loss and patient outcome (OS, p = 0.89; TTLRF, p = 0.21). No significant relationship was found between p16INK4A status and ATM loss, for patient outcome. We found 35.6% (n = 26) of patients demonstrated polysomy of chromosome 11 (defined as the presence of a mean >2.5 copies of chromosome 11) which was significantly associated with p16INK4A negative status (p = 0.0004), but did not influence outcome.

Conclusions

ATM loss is a frequent event in HNSCC, however it does not impact outcome after treatment with chemoradiation. Polysomy of chromosome 11 was significantly associated with p16INK4A negative status but also lacks prognostic significance.

Introduction

The Ataxia-Telangiectasia-Mutated (ATM) gene is a tumour suppressor gene located on 11q22 that encodes a serine-threonine kinase that is involved in double-stranded DNA damage repair and cell cycle control. Loss of ATM gene function is associated with an increased risk of malignancy and has been implicated in radiation treatment failure and poor prognosis in head and neck squamous cell carcinomas (HNSCC).[1], [2], [3]

Homozygous loss of function of the ATM gene results in a rare autosomally recessive inherited condition called Ataxia-Telangiectasia (A-T). Patients with A-T have a clinical phenotype which includes cerebellar ataxia, occulo-cutaneous telangiectasia, immunosuppression, premature aging, increased risk of malignancies and marked radiosensitivity. They also manifest a cellular phenotype with cell cycle check point defects, increased chromosomal instability and radiosensitivity.[4], [5] ATM is a critical member of the DNA repair pathway with complex protein–protein interactions facilitating recognition of double-stranded DNA breaks, recruitment of DNA repair proteins and activation of cell cycle check points to enable repair to occur. ATM activation involves interaction with the MRE11-RAD50-NBS1 (MRN) complex to trigger downstream cell cycle check point activation through phosphorylation of CHK24 and other important substrates including p53.[6], [7], [8] Chemical inhibitors of ATM have also been shown to result in cellular radiosensitivity.9 The loss of one copy of the ATM gene can also manifest with intermediate radiation sensitivity compared with homozygous ATM loss10, though this not a consistent finding from in vivo and in vitro studies of A-T heterozygotes or cell line studies.[2], [10], [11], [12], [13], [14], [15]

Several lines of evidence support the clinical significance of ATM gene loss in HNSCC. Lazar and colleagues were first to demonstrate a 25% incidence of loss of heterozygosity (LOH) of 11q23, a region that includes the ATM locus, in patients with HNSCC, which correlated with an increased risk of disease recurrence (p = 0.04, Fisher’s exact test) and resistance to radiotherapy.3 Ai and colleagues demonstrated that 25% of their patients studied with HNSCC harboured ATM gene promoter hypermethylation.1 The presence of promoter methylation was significantly associated with poorer overall 5-year survival (HR 1.44, Log-rank p = 0.03). In vitro studies in HNSCC cell line studies utilising fluorescence in-situ hybridization (FISH) unexpectedly demonstrated a correlation between distal 11q loss, including ATM loss, with radioresistance.2

Based on these data, we hypothesised that loss of ATM gene function may contribute poor prognosis after chemoradiation. Using FISH we retrospectively assessed the correlation between ATM gene loss with patient outcome, in 87 patients with locally advanced HNSCC who had been treated at a single institution with chemoradiotherapy.

Given the known significance of HPV/p16INK4A positive status in conferring a favourable prognosis in oropharyngeal HNSCC16 regardless of treatment modality, we also sought to determine whether the loss of ATM gene correlated with outcome in this subgroup.

Section snippets

Patients

The study population consisted of 87 patients enroled at the Peter MacCallum Cancer Center in successive clinical trials that have previously been reported.[17], [18], [19] Treatment protocols consisted of definitive radiotherapy administered with cisplatin plus tirapazamine (Phase I), cisplatin plus tirapazamine or cisplatin/5FU (Phase II), or cisplatin plus tirapazamine or high dose cisplatin alone (Phase III). The phase II and III trials were conducted under the auspices of the Trans-Tasman

Results

Of 87 patients, FISH of the ATM gene was informative in 73 patients (Fig. 1 and Supplementary Table 1). The median time to follow up was 6.2 years (range 4.0–11.5 years). Patient characteristics and tumour characteristics are detailed in Table 1. Patients were predominantly male (n = 63, 86.3%) with a mean age of 56.6 years, of favourable ECOG performance status (n = 46, 63.0% for ECOG 0), with a preponderance of oropharyngeal tumours (n = 51, 69.9%). ATM loss was found in 60.3% (44/73) of patients.

Discussion

To our knowledge, this is the largest study investigating the relationship between ATM gene loss detected by FISH with clinical correlation, in patients treated for locally advanced HNSCC. We were able to demonstrate that loss of ATM is a frequent event in HNSCC but we found no correlation with outcome. We are also the first to report on the significant relationship between p16INK4A negative oropharyngeal disease and the presence of polysomy of chromosome 11, although this did not impact on

Role of the funding source

N/A.

Conflict of interest statement

The authors have no conflicts of interest to declare.

Acknowledgements

Nil.

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