Potential Role of Single Nucleotide Polymorphisms of XRCC1, XRCC3, and RAD51 in Predicting Acute Toxicity in Rectal Cancer Patients Treated With Preoperative Radiochemotherapy

Molecular mechanisms of sensitivity and resistance to radiotherapy

The molecular mechanisms underlying sensitivity and resistance to radiotherapy is an area of active investigation and discovery as its clinical applications have the potential to improve cancer patients' outcomes. In addition to the traditional pathways of radiation biology, our knowledge now includes molecular pathways of radiation sensitivity and resistance which have provided insights into potential targets for enhancing radiotherapy efficacy. Sensitivity to radiotherapy is influenced by the intricate interplay of various molecular mechanisms involved in DNA damage repair, apoptosis, cellular senescence, and epigenetics. Translationally, there have been several successful applications of this new knowledge into the clinic, such as biomarkers for improved response to chemo-radiation. New therapies to modify radiation response, such as the poly (ADP-ribose) polymerase (PARP) inhibitors, derived from research on DNA repair pathways leading to radiotherapy resistance, are being used clinically. In addition, p53-mediated pathways are critical for DNA damage related apoptosis, cellular senescence, and cell cycle arrest. As the understanding of genetic markers, molecular profiling, molecular imaging, and functional assays improve, these advances once translated clinically, will help propel modern radiation therapy towards more precise and individualized practices.

Variability of DNA Repair and Oxidative Stress Genes Associated with Worst Pain in Breast Cancer Survivors on Aromatase Inhibitors

Pain is a problem affecting women with breast cancer (HR+BrCa) receiving aromatase inhibitor (AI) therapy. We investigated the relationship between single-nucleotide polymorphisms (SNPs) in DNA repair and oxidative stress genes and perceived worst pain after 6 months of AI therapy. We explored 39 SNPs in genes involved in DNA repair (ERCC2, ERCC3, ERCC5, and PARP1) and oxidative stress (CAT, GPX1, SEPP1, SOD1, and SOD2) in women with HR+BrCa receiving adjuvant therapy (AI ± chemotherapy; n = 138). Pain was assessed via the Brief Pain Inventory. Hurdle regression was used to evaluate the relationship between each associated allele and (1) the probability of pain and (2) the severity of worst pain. ERCC2rs50872 and ERCC5rs11069498 were associated with the probability of pain and had a significant genetic risk score (GRS) model (p = 0.003). ERCC2rs50872, ERCC5rs11069498, ERCC5rs4771436, ERCC5rs4150360, PARP1rs3219058, and SEPP1rs230819 were associated with the severity of worst pain, with a significant GRS model (conditional mean estimate = 0.45; 95% CI = 0.29, 0.60; p < 0.001). These results suggest DNA repair and oxidative stress pathways may play a role in the probability of pain and the severity of worst pain. As healthcare delivery moves towards the model of precision healthcare, nurses may, in the future, be able to use these results to tailor patient care based on GRS.

The kinetics of blast clearance are associated with copy number alterations in childhood B-cell acute lymphoblastic leukemia

We analyzed the pattern of whole-genome copy number alterations (CNAs) and their association with the kinetics of blast clearance during the induction treatment among 195 pediatric patients with B-cell precursor acute lymphoblastic leukemia (BCP-ALL) who displayed intermediate or high levels of minimal residual disease (MRD). Using unsupervised hierarchical clustering of CNAs > 5 Mbp, we dissected three clusters of leukemic samples with distinct kinetics of blast clearance [A - early slow responders (n=105), B - patients with persistent leukemia (n=24), C - fast responders with the low but detectable disease at the end of induction (n=66)] that corresponded with the patients' clinical features, the microdeletion profile,the presence of gene fusions and patients survival. Low incidence of large CNAs and chromosomal numerical aberrations occurred in cluster A which included ALL samples showing recurrent microdeletions within the genes encoding transcription factors (i.e., IKZF1, PAX5, ETV6, and ERG), DNA repair genes (XRCC3 and TOX), or harboring chromothriptic pattern of CNAs. Low hyperdiploid karyotype with trisomy 8 or hypodiploidy was predominantly observed in cluster B. Whereas cluster C included almost exclusively high-hyperdiploid ALL samples with concomitant mutations in RAS pathway genes. The pattern of CNAs influences the kinetics of leukemic cell clearance and selected aberrations affecting DNA repair genes may contribute to BCP-ALL chemoresistance.

NBN, RAD51 and XRCC3 Polymorphisms as Potential Predictive Biomarkers of Adjuvant Radiotherapy Toxicity in Early HER2-Positive Breast Cancer

Simple Summary

Adjuvant radiotherapy for breast cancer patients significantly improves survival and causes side effects. It is known that the response to radiotherapy is individual, but we are not yet able to predict patients with high risk for acute or late radiotherapy adverse events. This study aimed to investigate the association between homologous recombination repair (HRR) polymorphisms and radiotherapy toxicity and thus contribute to the knowledge on potential predictive biomarkers of radiotherapy toxicity in early HER2-positive breast cancer. This study was among the first to evaluate the role of HRR genetic variability with cardiac toxicity. RAD51 polymorphisms were associated with cardiac adverse events, while XRCC3 polymorphisms were associated with skin adverse events. Our results suggest that polymorphisms in key HRR genes might be used as potential biomarkers of late treatment-related adverse events in early HER2-positive breast cancer treated with radiotherapy.

Abstract

Radiotherapy (RT) for breast cancer significantly impacts patient survival and causes adverse events. Double-strand breaks are the most harmful type of DNA damage associated with RT, which is repaired through homologous recombination (HRR). As genetic variability of DNA repair genes could affect response to RT, we aimed to evaluate the association of polymorphisms in HRR genes with tumor characteristics and the occurrence of RT adverse events in early HER2-positive breast cancer. Our study included 101 breast cancer patients treated with adjuvant RT and trastuzumab. All patients were genotyped for eight single nucleotide polymorphisms in NBN, RAD51 and XRCC3 using competitive allele-specific PCR. Carriers of XRCC3 rs1799794 GG genotype were less likely to have higher tumor differentiation grade (OR = 0.05, 95% CI = 0.01–0.44, p = 0.007). Carriers of RAD51 rs1801321 TT genotype were more likely to have higher NYHA class in univariable (OR = 10.0; 95% CI = 1.63–61.33; p = 0.013) and multivariable (OR = 9.27; 95% CI = 1.28–67.02; p = 0.027) analysis. Carriers of RAD51 rs12593359 GG genotype were less likely to have higher NYHA class in univariable (OR = 0.09; 95% CI = 0.01–0.79; p = 0.030) and multivariable (OR = 0.07; 95% CI = 0.01–0.81; p = 0.034) analysis. Carriers of XRCC3 rs1799794 GG genotypes experienced more skin adverse events based on LENT-SOMA scale in univariable (OR = 5.83; 95% CI = 1.22–28.00; p = 0.028) and multivariable (OR = 10.90; 95% CI = 1.61–73.72; p = 0.014) analysis. In conclusion, XRCC3 and RAD51 polymorphisms might contribute to RT adverse events in early HER2-positive breast cancer patients.

Novel MEIOB variants cause primary ovarian insufficiency and non-obstructive azoospermia

Background: Infertility is a global health concern. MEIOB has been found to be associated with premature ovarian insufficiency (POI) and non-obstructive azoospermia (NOA), but its variants have not been reported in Chinese patients. The aim of this study was to identify the genetic aetiology of POI or NOA in three Han Chinese families. Methods: Whole-exome sequencing (WES) was used to identify candidate pathogenic variants in three consanguineous Chinese infertile families with POI or NOA. Sanger sequencing was performed to validate these variants in the proband of family I and her affected family members. In vitro functional analyses were performed to confirm the effects of these variants. Results: Two novel homozygous frameshift variants (c.258_259del and c.1072_1073del) and one novel homozygous nonsense variant (c.814C > T) in the MEIOB gene were identified in three consanguineous Han Chinese families. In vitro functional analyses revealed that these variants produced truncated proteins and affected their function. Conclusion: We identified three novel MEIOB loss-of-function variants in local Chinese patients for the first time and confirmed their pathogenicity using in vitro functional analyses. These results extend the mutation spectrum of the MEIOB gene and have important significance for genetic counselling in these families.

Predictive value of clinical toxicities of chemotherapy with fluoropyrimidines and oxaliplatin in colorectal cancer by DPYD and GSTP1 gene polymorphisms

BACKGROUND

Fluoropyrimidines and platinum are still widely used for colorectal cancer (CRC) management. Several studies have reported that mutations of dihydropyrimidine dehydrogenase (DPYD) and glutathione S-transferase pi-1 (GSTP1) polymorphisms are related to chemotherapy-related adverse events. In the present study, we purposed to assess the impact of DPYD and GSTP1 variants on the toxicity of adjuvant chemotherapy risk among the Hakka population, minimize adverse events, and to maximize therapy outcome for individualized treatment.

METHODS

Genotyping was examined in 104 patients diagnosed with CRC cases and receiving fluoropyrimidine and platinum drug-based chemotherapy regimen by direct sequencing of DPYD and GSTP1 polymorphisms. Three DPYD variants including *2A, *5A, *9A, and GSTP1 c.313A>G were analyzed and clinical outcomes were assessed.

RESULTS

The data suggest that the incidence of DPYD*5A, DPYD*9A, and GSTP1 c.313A>G variants were 38.4%, 24%, and 32.7%, respectively. DPYD*2A variant was not found. A total of 23 patients (22.1%) suffered severe vomiting and 19 patients (18.3%) suffered severe anemia. DPYD*5A polymorphism was found significantly associated with grade 3/4 ulceration (p = 0.001). GSTP1 was determined to be an independent risk factor for severe vomiting and skin ulceration (p = 0.042 and p = 0.018, respectively). Patients with GSTP1 c. 313A>G mutant type contributed to a higher risk for grade severe toxicity compared with wild genotype (p = 0.027). Nevertheless, no significant difference was found between patients with DPYD*2A, *5A, and *9A for chemotherapeutic toxicity.

CONCLUSIONS

The results demonstrated that GSTP1 polymorphisms were useful predictors of severe events. Screening of single-nucleotide polymorphisms of GSTP1 in colorectal cancer patients before chemotherapy may help to realize personalized therapy.

Germline and Somatic Pharmacogenomics to Refine Rectal Cancer Patients Selection for Neo-Adjuvant Chemoradiotherapy

Neoadjuvant chemoradiotherapy (nCRT) followed by radical surgery is the standard of care for patients with Locally Advanced Rectal Cancer (LARC). Current selection for nCRT is based on clinical criteria regardless of any molecular marker. Pharmacogenomics may be a useful strategy to personalize and optimize nCRT in LARC. This review aims to summarize the most recent and relevant findings about the role of germline and somatic pharmacogenomics in the prediction of nCRT outcome in patients with LARC, discussing the state of the art of their application in the clinical practice. A systematic literature search of the PubMed database was completed to identify relevant English-language papers published up to January 2020. The chemotherapeutic backbone of nCRT is represented by fluoropyrimidines, mainly metabolized by DPD (Dihydro-Pyrimidine Dehydrogenase, DPYD). The clinical impact of testing DPYD*2A, DPYD*13, c.2846A > T and c.1236G > A-HapB3 before a fluoropyrimidines administration to increase treatment safety is widely acknowledged. Other relevant target genes are TYMS (Thymidylate Synthase) and MTHFR (Methylene-Tetrahydro-Folate Reductase), whose polymorphisms were mainly studied as potential markers of treatment efficacy in LARC. A pivotal role of a TYMS polymorphism in the gene promoter region (rs34743033) was reported and was pioneeringly used to guide nCRT treatment in a phase II study. The pharmacogenomic analysis of other pathways mostly involved in the cellular response to radiation damage, as the DNA repair and the activation of the inflammatory cascade, provided less consistent results. A high rate of somatic mutation in genes belonging to PI3K (Phosphatidyl-Inositol 3-Kinase) and MAPK (Mitogen-Activated Protein Kinase) pathways, as BRAF (V-raf murine sarcoma viral oncogene homolog B1), KRAS (Kirsten Rat Sarcoma viral oncogene homolog), NRAS (Neuroblastoma RAS viral (v-ras) oncogene homolog), PIK3CA (Phosphatidyl-Inositol-4,5-bisphosphate 3-Kinase, Catalytic Subunit Alpha), as well as TP53 (Tumor Protein 53) was reported in LARC. Their pharmacogenomic role, already defined in colorectal cancer, is under investigation in LARC with promising results concerning specific somatic mutations in KRAS and TP53, as predictors of tumor response and prognosis. The availability of circulating tumor DNA in plasma may also represent an opportunity to monitor somatic mutations in course of therapy.

Prediction of mucositis risk secondary to cancer therapy: a systematic review of current evidence and call to action

PURPOSE

Despite advances in personalizing the efficacy of cancer therapy, our ability to identify patients at risk of severe treatment side effects and provide individualized supportive care is limited. This is particularly the case for mucositis (oral and gastrointestinal), with no comprehensive risk evaluation strategies to identify high-risk patients. We, the Multinational Association for Supportive Care in Cancer/International Society for Oral Oncology (MASCC/ISOO) Mucositis Study Group, therefore aimed to systematically review current evidence on that factors that influence mucositis risk to provide a foundation upon which future risk prediction studies can be based.

METHODS

We identified 11,018 papers from PubMed and Web of Science, with 197 records extracted for full review and 113 meeting final eligibility criteria. Data were then synthesized into tables to highlight the level of evidence for each risk predictor.

RESULTS

The strongest level of evidence supported dosimetric parameters as key predictors of mucositis risk. Genetic variants in drug-metabolizing pathways, immune signaling, and cell injury/repair mechanisms were also identified to impact mucositis risk. Factors relating to the individual were variably linked to mucositis outcomes, although female sex and smoking status showed some association with mucositis risk.

CONCLUSION

Mucositis risk reflects the complex interplay between the host, tumor microenvironment, and treatment specifications, yet the large majority of studies rely on hypothesis-driven, single-candidate approaches. For significant advances in the provision of personalized supportive care, coordinated research efforts with robust multiplexed approaches are strongly advised.

Disease course of lung oligometastatic colorectal cancer treated with stereotactic body radiotherapy

PURPOSE

Stereotactic body radiotherapy (SBRT) or stereotactic ablative radiotherapy (SABR) has been shown to increase survival rates in oligometastatic disease (OMD), but local control of colorectal metastases remains poor. We aimed to explore the natural course of oligometastatic colorectal cancer and to investigate how SBRT of lung metastases can delay the progression to polymetastatic disease (PMD).

METHODS

107 lung oligometastases in 38 patients were treated with SBRT at a single institution. The median number of treated lesions was 2 (range 1-5). Time to PMD (ttPMD) was defined as the time from SBRT to the occurrence of >5 new metastases. Genetic biomarkers such as EGFR, KRAS, NRAS, BRAF, and microsatellite instability were investigated as predictive factors for response rates.

RESULTS

Median follow-up was 28 months. At median follow-up, 7 patients were free from disease and 31 had progression: 18 patients had sequential oligometastatic disease (SOMD) and 13 polymetastatic progression. All SOMD cases received a second SBRT course. Median progression-free survival (PFS) was 7 months (range 4-9 months); median ttPMD was 25.8 months (range 12-39 months) with 1‑ and 2‑year PFS rates of 62.5% and 53.4%, respectively. 1‑ and 2‑year local PFS (LPFS) rates were 91.5% and 80%, respectively. At univariate analysis, BRAF wildtype correlated with better LPFS (p = 0.003), SOMD after primary SBRT was associated with longer cancer-specific survival (p = 0.031). Median overall survival (OS) was 39.5 months (range 26-64 months) and 2‑year OS was 71.1%.

CONCLUSION

The present results support local ablative treatment of lung metastases using SBRT in oligometastatic colorectal cancer patients, as it can delay the transition to PMD. Patients who progressed as SOMD maintained a survival advantage compared to those who developed PMD.

Association Between Polymorphisms in DNA Damage Repair Genes and Radiation Therapy-Induced Early Adverse Skin Reactions in a Breast Cancer Population: A Polygenic Risk Score Approach

PURPOSE

Genetic variations in DNA damage repair (DDR) genes may influence radiation therapy (RT)-induced acute normal tissue toxicity in patients with breast cancer. Identifying an individual or multiple single-nucleotide polymorphisms (SNPs) associated with RT-induced early adverse skin reactions (EASR) is critical for precision medicine in radiation oncology.

METHODS AND MATERIALS

At the completion of RT, EASR was assessed using the Oncology Nursing Society scale (0-6) in 416 patients with breast cancer, and Oncology Nursing Society score ≥4 was considered RT-induced EASR. PLINK set-based tests and subsequent individual SNP association analyses were conducted to identify genes and SNPs associated with EASR among the 53 DDR genes and 1968 SNPs. A weighted polygenic risk score (PRS) model was constructed to ascertain the association between the joint effect of risk alleles and EASR.

RESULTS

The study population consisted of 264 Hispanic whites, 86 blacks or African Americans, 55 non-Hispanic whites, and 11 others. A total of 115 patients (27.6%) developed EASR. Five genes (ATM, CHEK1, ERCC2, RAD51C, and TGFB1) were significantly associated with RT-induced EASR. Nine SNPs within these 5 genes were further identified: ATM rs61915066, CHEK1 rs11220184, RAD51C rs302877, rs405684, TBFB1 rs4803455, rs2241714, and ERCC2 rs60152947, rs10404465, rs1799786. In a multivariable-adjusted PRS model, patients in a higher quartile of PRS were more likely to develop EASR compared with patients in the lowest quartile (OR_{q2 vs.q1} = 1.94, 95% CI, 0.86-4.39; OR_{q3 vs.q1} = 3.46, 95% CI, 1.57-7.63; OR_{q4 vs.q1} = 8.64, 95% CI, 3.92-19.02; and P_trend < .0001).

CONCLUSIONS

We newly identified the associations between 9 SNPs in ATM, CHEK1, RAD51C, TGFB1, and ERCC2 and RT-induced EASR. PRS modeling showed its potential in identifying populations at risk. Multiple SNPs in DDR genes may jointly contribute to interindividual variation in RT-induced EASR. Validation in an independent external cohort is required to determine the clinical significance of these predictive biomarkers.

Role of Rad51 and DNA repair in cancer: A molecular perspective

The maintenance of genome integrity is essential for any organism survival and for the inheritance of traits to offspring. To the purpose, cells have developed a complex DNA repair system to defend the genetic information against both endogenous and exogenous sources of damage. Accordingly, multiple repair pathways can be aroused from the diverse forms of DNA lesions, which can be effective per se or via crosstalk with others to complete the whole DNA repair process. Deficiencies in DNA healing resulting in faulty repair and/or prolonged DNA damage can lead to genes mutations, chromosome rearrangements, genomic instability, and finally carcinogenesis and/or cancer progression. Although it might seem paradoxical, at the same time such defects in DNA repair pathways may have therapeutic implications for potential clinical practice. Here we provide an overview of the main DNA repair pathways, with special focus on the role played by homologous repair and the RAD51 recombinase protein in the cellular DNA damage response. We next discuss the recombinase structure and function per se and in combination with all its principal mediators and regulators. Finally, we conclude with an analysis of the manifold roles that RAD51 plays in carcinogenesis, cancer progression and anticancer drug resistance, and conclude this work with a survey of the most promising therapeutic strategies aimed at targeting RAD51 in experimental oncology.

Positive effect of single nucleotide RAD51 135G>C polymorphism and low Ku70 protein expression on female rectal cancer patients survival after preoperative radiotherapy

BACKGROUND/AIMS

This is a retrospective analysis of 103 patients having locally advanced rectal cancer who received short-course radiotherapy (SCRT). The objective of the study was to check whether a polymorphism in the RAD51 gene (135 G>C), Ku70 protein expression, and tumor microenvironment: proliferation rate measured by BrdUrdLI and Ki-67LI, hypoxia (glucose transporter-1 expression), P53 protein expression, and DNA ploidy can influence DNA repair capacity, the factors contributing to patient overall survival (OS) and the incidence of recurrences and metastases.

MATERIALS AND METHODS

RAD51 (135 G>C) polymorphism was evaluated using restriction fragment length polymorphism polymerase chain reaction, and proteins were identified using immunohistochemistry.

RESULTS

There were 3 (2.9%) tumors with RAD51 CC, 75 (72.8%) with GG, and 25 (24.3%) with GC genotypes. The median follow-up time was 63.1 months (range 2-120). Patients with CC genotype survived significantly longer than those with GG and GC genotypes and did not develop any recurrences or distant metastases. Female patients with Ku70 expression (<75.1) or RAD51CC genotype (impaired DNA damage repair and radiosensitive) had significantly longer OS (p=0.013) than those with Ku70>75.1 % or RAD51GG,GC (radioresistant phenotype) and male patients in the log-rank test. In multivariate analysis, positive prognostic factors for OS in the male patients were grade=1 and <17 days break in the treatment, whereas in the female subgroup, only radiosensitive phenotype (Ku70 <75.1% or RAD51CC genotype).

CONCLUSION

To the best of our knowledge, this is the first study to provide evidence for the positive effect of CC genotype of RAD51 or low Ku70 expression on OS in females with rectal cancer after SCRT.

Single nucleotide polymorphism of <italic>GSTP1</italic> and pathological complete response in locally advanced rectal cancer patients treated with neoadjuvant concomitant radiochemotherapy

Purpose

Standard treatment for locally advanced rectal cancer consists of neoadjuvant radiochemotherapy with concomitant fluoropyrimidine or oxaliplatin and surgery with curative intent. Pathological complete response has shown to be predictive for better outcome and survival; nevertheless there are no biological or genetic factors predictive for response to treatment. We explored the correlation between the single nucleotide polymorphisms (SNPs) GSTP1 (A313G) and XRCC1 (G28152A), and the pathological complete response and survival after neoadjuvant radiochemotherapy in locally advanced rectal cancer patients.

Materials and Methods

Genotypes GSTP1 (A313G) and XRCC1 (G28152A) were determined by pyrosequencing technology in 80 patients affected by locally advanced rectal cancer.

Results

The overall rate of pathological complete response in our study population was 18.75%. Patients homozygous AA for GSTP1 (A313G) presented a rate of pathological complete response of 26.6% as compared to 8.5% of the AG+GG population (p = 0.04). The heterozygous comparison (AA vs. AG) showed a significant difference in the rate of pathological complete response (26.6% vs. 6.8%; p = 0.034). GSTP1 AA+AG patients presented a 5- and 8-year cancer-specific survival longer than GSTP1 GG patients (87.7% and 83.3% vs. 44.4% and 44.4%, respectively) (p = 0.014). Overall survival showed only a trend toward significance in favor of the haplotypes GSTP1 AA+AG. No significant correlations were found for XRCC1 (G28152A).

Conclusion

Our results suggest that GSTP1 (A313G) may predict a higher rate of pathological complete response after neoadjuvant radiochemotherapy and a better outcome, and should be considered in a more extensive analysis with the aim of personalization of radiation treatment.

RAD51 as a potential surrogate marker for DNA repair capacity in solid malignancies

Targeting deficient mechanisms of cellular DNA repair still represents the basis for the treatment of the majority of solid tumors, and increased DNA repair capacity is a hallmark mechanism of resistance not only to DNA-damaging treatments such as cytotoxic drugs and radiotherapy, but also to small molecule targeted drugs such as inhibitors of poly-ADP ribose polymerase (PARP). Hence, there is substantial medical need for potent and convenient biomarkers of individual response to DNA-targeted treatment in personalized cancer care. RAD51 is a highly conserved protein that catalyzes DNA repair via homologous recombination, a major DNA repair pathway which directly modulates cellular sensitivity to DNA-damaging treatments. The clinical and biological significance of RAD51 protein expression is still under investigation. Pre-clinical studies consistently show the important role of nuclear RAD51 immunoreactivity in chemo- and radioresistance. Validating data from clinical trials however is limited at present, and some clinical studies show controversial results. This review gives a comprehensive overview on the current knowledge about the prognostic and predictive value of RAD51 protein expression and genetic variability in patients with solid malignancies.

XRCC3 is a promising target to improve the radiotherapy effect of esophageal squamous cell carcinoma

Radiotherapy is widely applied for treatment of esophageal squamous cell carcinoma (ESCC). The Rad51-related protein XRCC3 plays roles in the recombinational repair of DNA double-strand breaks to maintain chromosome stability and repair DNA damage. The present study aimed to investigate the effect of XRCC3 on the radiotherapy response of ESCC and the underlying mechanisms of the roles of XRCC3 in ESCC radiosensitivity. XRCC3 expression in ESCC cells and tissues was higher than that in normal esophageal epithelial cells and corresponding adjacent noncancerous esophageal tissue. High XRCC3 expression was positively correlated with resistance to chemoradiotherapy in ESCC and an independent predictor for short disease-specific survival of ESCC patients. Furthermore, the therapeutic efficacy of radiotherapy in vitro and in vivo was substantially increased by knockdown of XRCC3 in ESCC cells. Ectopic overexpression of XRCC3 in both XRCC3-silenced ESCC cells dramatically enhanced ESCC cells' resistance to radiotherapy. Moreover, radiation resistance conferred by XRCC3 was attributed to enhancement of homologous recombination, maintenance of telomere stability, and a reduction of ESCC cell death by radiation-induced apoptosis and mitotic catastrophe. Our data suggest that XRCC3 protects ESCC cells from ionizing radiation-induced death by promoting DNA damage repair and/or enhancing telomere stability. XRCC3 may be a novel radiosensitivity predictor and promising therapeutic target for ESCC.