Background: It has been hypothesized that patient to patient variation in normal tissue reactions to radiotherapy is associated with the presence of polymorphic variations in genes involved in DNA repair.
Purpose: To test for a possible association between two single-nucleotide polymorphisms (SNPs), XRCC1 399 G>A Arg/Gln and XRCC3 241 C>T Thr/Met and late reactions to radiotherapy.
Patients and methods: In this case control study, 50 Head and Neck cancer patients were retrospectively recruited. The grade (G) of fibrosis, a late complication to radiotherapy, was scored using the RTOG/EORTC grading system. Radiosensitive patients with moderate to severe subcutaneous and deep tissue fibrosis (cases, G2-3, n=25) where matched with patients with minimal fibrotic reactions (control, G0-1, n=25). The two nonsynonymous SNPs were genotyped by direct sequencing of DNA extracted from blood or cultured fibroblasts.
Results: Allelic frequency showed significant association with grade of fibrosis for XRCC1 399 G/A (p=0.05), but not for XRCC3 241 C>T (p=0.10).
Conclusions: This pilot study corroborates the association between XRCC1 399 G>A and risk of late normal tissue complications following radiotherapy in our patients. Large studies are required to unravel more SNPs that can influence radiosensitivity and ascertain the associations with reactions to radiotherapy in order to be used as genetic predictive biomarkers of individual radiosensitivity.
Key words: Single nucleotide polymorphism - Radiosensitivity - Late reactions to radiotherapy - XRCC1 - XRCC3.