Molecular genetics of RT side-effectsNo association between SNPs regulating TGF-β1 secretion and late radiotherapy toxicity to the breast: Results from the RAPPER study☆
Section snippets
Materials and methods
The patient characteristics and radiotherapy technique used in the Cambridge Breast IMRT trial have been previously described [2]. In this study 778 women, with operable unilateral histological-confirmed breast cancer (T1-3, N0-1, M0 at presentation) or ductal carcinoma in situ (DCIS) requiring radiotherapy after complete macroscopic excision of the tumour by breast conserving surgery (no implants), were treated either with forward-planned IMRT or standard 2-field radiotherapy. A standard plan
Study end-points
The primary end-point of the Cambridge Breast IMRT trial was photographic assessment of late cosmetic effects. Frontal photographs of both breasts were taken after primary surgery and before the start of radiotherapy, and repeated at 2 years after treatment. Two photographs were taken, one with the hands resting on the hips, the other with the arms raised above the head. Follow-up photographs were terminated in the case of local tumour relapse, further breast surgery, declining health or patient
Genotyping
DNA was extracted from the blood samples by Tepnel Life Sciences (www.tepnel.com). High-quality DNA was extracted from >99% of samples, with an average yield of 195 ± 67 μg (range 22–494 μg). All samples were genotyped using the Taqman 7900HT Sequence Detection System according to manufacturer’s instructions. Each assay was carried out using 10 ng DNA in a 5 μL reaction using Taqman Universal PCR Master Mix (Applied Biosystems, Warrington, United Kingdom), forward and reverse-primers and FAM- and
Statistical analysis
Polychotomous logistic regression was used to relate genotype with photographic and clinical assessment scores. Polychotomous logistic regression, also known as ordinal response regression, was considered most appropriate for analysing the data as the dependent variables (toxicity end-points) take multiple ordered values. No numeric relationship is assumed between these grades; it is only assumed that lower grades correspond to milder reactions. Patients are assumed to have a decreasing risk of
Results
Late clinical assessment data and genotype were available for 778 participants; photographic data were available for 703 study participants. Patient questionnaire data were available in 681 patients. Analysis was performed on all 778 patients; therefore some patients had missing values for some end-points. On photographic assessment, 210 patients (27%) showed some degree of breast shrinkage, whilst 45 patients (6%) showed marked breast shrinkage. The mean age of the patients was 59 years (range
Discussion
This large, purpose designed study has been unable to confirm recent reports of significant associations between the TGFB1 (C-509T) SNP and increased risk of radiation fibrosis [20], [21], [22]. We did not find a significant association between either of the correlated TGFB1 SNPs, L10P (rs1800470) or C-509T (rs1800469), with the development of induration, assessed by the clinician. Induration of the breast is the clinical end-point used to assess the pathological process of fibrosis.
Conclusion
Our finding emphasises the need for trials of sufficient size to have rigorous statistical power. It also illustrates a common problem, found with most other human genetic traits; that is, an iterative candidate gene approach is not an efficient methodology for discovering genetic determinants of variation. In traits where the common-variant-common-disease model holds, or at least contributes, well-designed genome-wide association scan (GWAS) methodology has proved more efficient and definitive
Acknowledgements
Dr. Gill Barnett is funded by a fellowship from Cancer Research UK and The Royal College of Radiologists. The Breast Cancer Campaign provides funding for the Cambridge Breast IMRT Trial radiographer, Jennifer Wilkinson and Cancer Research UK funds the RAPPER study. Alison Dunning is funded by CR-UK and Paul Pharoah is a Senior Clinical Research Fellow of CR-UK. Dr. Neil Burnet and Dr. Charlotte Coles are supported by the NIHR Cambridge Biomedical Research Centre. Professor Catharine West also
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2016, Cancer LettersCitation Excerpt :However, a more recent, larger study showed a significantly increased risk of fibrosis in breast RT patients with telangiectasia, although overall, the risk of developing fibrosis was much lower than that of telangiectasia [35]. In the RAPPER (“Radiogenomics: Assessment of Polymorphisms for Predicting the Effects of Radiotherapy”) study, which comprises 778 breast RT patients enrolled in the Cambridge breast IMRT (intensity-modulated RT) trial, correlation coefficients were generally low, although significant correlations were found between several end points (e.g. between breast shrinkage and six other end points, as well as between breast induration, edema, and telangiectasia) but not between breast induration and telangiectasia [36]. The lack of close correlations between different end points, in particular between radiation-induced fibrosis and telangiectasia, supports the view that there are differences in the mechanisms underlying the pathogenesis of different end points.
A preliminary study on racial differences in HMOX1, NFE2L2, and TGFβ1 gene polymorphisms and radiation-induced late normal tissue toxicity
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2014, Clinical OncologyCitation Excerpt :Combined data from two British cohorts published at the same time showed a significant association of the −509 T allele with fibrosis [42,57], whereas a further study showed an association with the 869 T > C allele [43]. More recently, the large British RAPPER cohort of breast and prostate cancer patients and a cohort of Spanish prostate cancer patients failed to confirm any association of TGFB1 genotypes with radiation toxicity [58,59]. This negative finding was further substantiated in a meta-analysis of 2782 participants from 11 cohorts [60].
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On behalf of the Cambridge Breast IMRT Trial Investigators.