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Original Investigation
December 2018

Association of Transforming Growth Factor β Polymorphism C−509T With Radiation-Induced Fibrosis Among Patients With Early-Stage Breast Cancer: A Secondary Analysis of a Randomized Clinical Trial

Author Affiliations
  • 1Division of Radiation Oncology, Department of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston
  • 2Department of Radiation Medicine, Oregon Health and Science University, Portland
  • 3Division of Cancer Prevention, Department of Health Services Research, The University of Texas MD Anderson Cancer Center, Houston
JAMA Oncol. 2018;4(12):1751-1757. doi:10.1001/jamaoncol.2018.2583
Key Points

Question  Does an association exist between C−509T polymorphism of the TGFB1 gene and radiotherapy-induced toxicity of normal breast tissue among women with pathologically confirmed stage 0 to IIA breast cancer treated with breast-conserving surgery and whole-breast irradiation?

Findings  This prospective cohort study evaluating 174 participants in a randomized clinial trial found grade 2 or higher breast fibrosis 3 years after radiotherapy in 13.8% of patients with the C−509T variant allele vs 3.8% of patients without the variant allele, a significant difference.

Meaning  The C−509T variant allele may be used prospectively as a genetic marker to identify patients at elevated risk for fibrosis following radiotherapy.

Abstract

Importance  Whether genetic factors can identify patients at risk for radiation-induced fibrosis remains unconfirmed.

Objective  To assess the association between the C−509T variant allele in the promoter region of TGFB1 and breast fibrosis 3 years after radiotherapy.

Design, Setting, and Participants  This is an a priori–specified, prospective, cohort study nested in an open-label, randomized clinical trial, which was conducted in community-based and academic cancer centers to compare hypofractionated whole-breast irradiation (WBI) (42.56 Gy in 16 fractions) with conventionally fractionated WBI (50 Gy in 25 fractions) after breast-conserving surgery. In total, 287 women 40 years or older with pathologically confirmed stage 0 to IIA breast cancer treated with breast-conserving surgery were enrolled from February 2011 to February 2014. Patients were observed for a minimum of 3 years. Outcomes were compared using the 1-sided Fisher exact test and multivariable logistic regression.

Exposures  A C-to-T single-nucleotide polymorphism at position −509 relative to the first major transcription start site (C−509T) of the TGFB1 gene.

Main Outcomes and Measures  The primary outcome was grade 2 or higher breast fibrosis as assessed using the Late Effects Normal Tissue/Subjective, Objective, Medical Management, Analytic scale (range, 0 to 3) three years after radiotherapy.

Results  Among 287 women enrolled in the trial, TGFB1 genotype and 3-year radiotherapy-induced toxicity data were available for 174 patients, of whom 89 patients (51%) with a mean (SD) age of 60 (8) years had at least 1 copy of C−509T. Grade 2 or higher breast fibrosis was present in 12 of 87 patients with C−509T (13.8%) compared with 3 of 80 patients without the allele variant (3.8%) (absolute difference, 10.0%; 95% CI, 1.7%-18.4%; P = .02). The results of multivariable analyses indicated that only C−509T (odds ratio, 4.47; 95% CI, 1.25-15.99; P = .02) and postoperative cosmetic outcome (odds ratio, 7.09; 95% CI, 2.41-20.90; P < .001) were significantly associated with breast fibrosis risk.

Conclusions and Relevance  To date, this study seems to be the first prospective validation of a genomic marker for radiation fibrosis. The C−509T allele in TGFB1 is a key determinant of breast fibrosis risk. Assessing TGFB1 genotype may facilitate a more personalized approach to locoregional treatment decisions in breast cancer.

Trial Registration  ClinicalTrials.gov identifier: NCT01266642

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