Reliable methods for identification of hypoxia in radiotherapy-treated tumors have been a desirable aim in radiation oncology for decades. Hypoxia is a common feature of the microenvironment in solid ...tumors, and it is associated with increased aggressiveness, reduced therapeutic response, and a poorer clinical outcome. In head and neck squamous cell carcinomas, the negative effect of hypoxia on radiotherapeutic response can be counteracted and minimized by applying hypoxic modification to radiotherapy, which favors the clinical outcome after treatment. However, not all tumors are hypoxic, hence not all patients benefit from the addition of hypoxic modification. Therefore, predictive and clinically applicable methods for pretherapeutic hypoxic evaluation and categorization are needed. Hypoxia gene expression signatures are a developing strategy to approach this obstacle. This method has evolved along with the development of complementary DNA microarray analysis and classifies tumors in accordance to the expression of specific hypoxia-responsive genes in the tumor biopsy. Thus, tumors are classified and categorized in terms of the biological behavior to hypoxic conditions in the microenvironment. Until now, most of the developed hypoxia signatures have only been evaluated in terms of their prognostic impact; however, recently, a predictive impact for hypoxic modification of radiotherapy was verified. Here, we provide an overview of the hypoxic issue in radiotherapy and present the most promising hypoxia gene expression signatures developed to date.
The aim of the study was to identify noninvasive markers of treatment-induced side effects. Reactive oxygen species (ROS) are generated after irradiation, and genetic variation in genes related to ...ROS metabolism might influence the level of radiation-induced adverse effects (AEs).
92 breast cancer (BC) survivors previously treated with hypofractionated radiation therapy were assessed for the AEs subcutaneous atrophy and fibrosis, costal fractures, lung fibrosis, pleural thickening, and telangiectasias (median follow-up time 17.1 years). Single-nucleotide polymorphisms (SNPs) in 203 genes were analyzed for association to AE grade. SNPs associated with subcutaneous fibrosis were validated in an independent BC survivor material (n=283). The influence of the studied genetic variation on messenger ribonucleic acid (mRNA) expression level of 18 genes previously associated with fibrosis was assessed in fibroblast cell lines from BC patients.
Subcutaneous fibrosis and atrophy had the highest correlation (r=0.76) of all assessed AEs. The nonsynonymous SNP rs1139793 in TXNRD2 was associated with grade of subcutaneous fibrosis, the reference T-allele being more prevalent in the group experiencing severe levels of fibrosis. This was confirmed in another sample cohort of 283 BC survivors, and rs1139793 was found significantly associated with mRNA expression level of TXNRD2 in blood. Genetic variation in 24 ROS-related genes, including EGFR, CENPE, APEX1, and GSTP1, was associated with mRNA expression of 14 genes previously linked to fibrosis (P≤.005).
Development of subcutaneous fibrosis can be associated with genetic variation in the mitochondrial enzyme TXNRD2, critically involved in removal of ROS, and maintenance of the intracellular redox balance.
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