Differential expression and prognostic value of ERCC1 and thymidylate synthase in resected gastric adenocarcinoma

Role of pH in Regulating Cancer Pyrimidine Synthesis

Replication is a fundamental aspect of cancer, and replication is about reproducing all the elements and structures that form a cell. Among them are DNA, RNA, enzymes, and coenzymes. All the DNA is doubled during each S (synthesis) cell cycle phase. This means that six billion nucleic acids must be synthesized in each cycle. Tumor growth, proliferation, and mutations all depend on this synthesis. Cancer cells require a constant supply of nucleotides and other macromolecules. For this reason, they must stimulate de novo nucleotide synthesis to support nucleic acid provision. When deregulated, de novo nucleic acid synthesis is controlled by oncogenes and tumor suppressor genes that enable increased synthesis and cell proliferation. Furthermore, cell duplication must be achieved swiftly (in a few hours) and in the midst of a nutrient-depleted and hypoxic environment. This also means that the enzymes participating in nucleic acid synthesis must work efficiently. pH is a critical factor in enzymatic efficiency and speed. This review will show that the enzymatic machinery working in nucleic acid synthesis requires a pH on the alkaline side in most cases. This coincides with many other pro-tumoral factors, such as the glycolytic phenotype, benefiting from an increased intracellular pH. An increased intracellular pH is a perfect milieu for high de novo nucleic acid production through optimal enzymatic performance.

Prognostic and Predictive Role of Excision Repair Cross-complementation Group 1 and Thymidylate Synthase in Colorectal Carcinoma Patients Received FOLFOX Chemotherapy: An Immunohistochemical Study

BACKGROUND AND STUDY AIMS

We aim to determine the frequency of thymidylate synthase (TS) and excision repair cross-complementation group 1 (ERCC-1) immunohistochemical (IHC) expression and its relationship with clinicopathologic variables in colorectal carcinoma (CRC) patients. In addition, we aim to assess the correlation between TS and ERCC-1 expression and the response of these cases to oxaliplatin and 5-fluorouracil chemotherapy (FOLFOX).

PATIENTS AND METHODS

Fifty-one CRC patients were prepared for IHC analysis of ERCC-1 and TS protein expression. All patients received oxaliplatin and 5-fluorouracil combined chemotherapy (FOLFOX) and were followed up for 24 months.

RESULTS

The data analysis showed that high ERCC-1 and TS expression was significantly associated with early treatment failure (P=0.020 and 0.000). In contrast, TS immunoexpression affects the disease-free survival rate (P=0.010). The presence of deep tumor invasion, distant metastasis, lymph node metastasis, and high Dukes' classification were significantly statistically associated with early treatment failure (P=0.001, 0.000, 0.041, and 0.015, respectively).

CONCLUSIONS

Our results showed that both ERCC-1 and TS are predictive factors for early treatment failure in CRC patients. TS protein is a prognostic factor for disease-free survival rates. This supports the theory that both ERCC-1 and TS can be used to improve chemotherapeutic outcomes in CRC patients. High expression of TS and ERCC-1 helps in the identification of cases that will get fewer benefits from FOLFOX chemotherapy. As an innovative strategy, in these cases, we can use alternative chemotherapeutic regimens or add an extra agent. In addition, Dukes' classification and lymph node metastasis are predictive factors for early treatment failure. Thus, all those values can be used to predict CRC patients with bad prognosis and those who will get fewer benefits from FOLFOX.

Identification of key genes and evaluation of clinical outcomes in lung squamous cell carcinoma using integrated bioinformatics analysis

Lung cancer is the leading cause of cancer-related mortality worldwide. Despite progress in the treatment of non-small-cell lung cancer, there are limited treatment options for lung squamous cell carcinoma (LUSC), compared with lung adenocarcinoma. The present study investigated the disease mechanism of LUSC in order to identify key candidate genes for diagnosis and therapy. A total of three gene expression profiles (GSE19188, GSE21933 and GSE74706) were analyzed using GEO2R to identify common differentially expressed genes (DEGs). The DEGs were then investigated using Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis. A protein-protein interaction (PPI) network was constructed via the Search Tool for the Retrieval of Interacting Genes/Proteins, and visualized using Cytoscape software. The expression levels of the hub genes identified using CytoHubba were validated using the University of California, Santa Cruz (UCSC) database and the Human Protein Atlas. A Kaplan-Meier curve and Gene Expression Profiling Interactive Analysis were then employed to evaluate the associated prognosis and clinical pathological stage of the hub genes. Furthermore, non-coding RNA regulatory networks were constructed using the Gene-Cloud Biotechnology information website. A total of 359 common DEGs (155 upregulated and 204 downregulated) were identified, which were predominantly enriched in 'mitotic nuclear division', 'cell division', 'cell cycle' and 'p53 signaling pathway'. The PPI network consisted of 257 nodes and 2,772 edges, and the most significant module consisted of 66 upregulated genes. A total of 19 hub genes exhibited elevated RNA levels, and 10 hub genes had elevated protein levels compared with normal lung tissues. The upregulation of five hub genes (CCNB1, CEP55, FOXM1, MKI67 and TYMS; defined in Table I) were significantly associated with poor overall survival and unfavorable clinical pathological stages. Various ncRNAs, such as C1orf220, LINC01561 and MGC39584, may also play important roles in hub-gene regulation. In conclusion, the present study provides further understanding of the pathogenesis of LUSC, and reveals CCNB1, CEP55, FOXM1, MKI67 and TYMS as potential biomarkers or therapeutic targets.

The use of DNA repair genes as prognostic indicators of gastric cancer

DNA repair genes can be used as prognostic biomarkers in many types of cancer. We aimed to identify prognostic DNA repair genes in patients with gastric cancer (GC) by systematically bioinformatic approaches using web-based database. Global gene expression profiles from altogether 1,325 GC patients' samples from six independent datasets were included in the study. Clustering analysis was performed to screen potentially abnormal DNA repair genes related to the prognosis of GC, followed by unsupervised clustering analysis to identify molecular subtypes of GC. Characteristics and prognosis differences were analyzed among these molecular subtypes, and modular key genes in molecular subtypes were identified based on changes in expression correlation. Multivariate Cox proportional hazard analysis was used to find the independent prognostic gene. Kaplan-Meier method and log-rank test was used to estimate correlations of key DNA repair genes with GC patients'overall survival. There were 57 key genes significantly associated to GC patients' prognosis, and patients were stratified into three molecular clusters based on their expression profiles, in which patients in Cluster 3 showed the best survival (P < 0.05). After a three-phase training, test and validation process, the expression profile of 13 independent key DNA repair genes were identified can classify the prognostic risk of patients. Compared with patients with low-risk score, patients with high risk score in the training set had shorter overall survival (P < 0.0001). Furthermore, we verified equivalent findings by these key DNA repair genes in the test set (P < 0.0001) and the independent validation set (P = 0.0024). Our results suggest a great potential for the use of DNA repair gene profiling as a powerful marker in prognostication and inform treatment decisions for GC patients.

GIT2-A keystone in ageing and age-related disease

Since its discovery, G protein-coupled receptor kinase-interacting protein 2, GIT2, and its family member, GIT1, have received considerable interest concerning their potential key roles in regulating multiple inter-connected physiological and pathophysiological processes. GIT2 was first identified as a multifunctional protein that is recruited to G protein-coupled receptors (GPCRs) during the process of receptor internalization. Recent findings have demonstrated that perhaps one of the most important effects of GIT2 in physiology concerns its role in controlling multiple aspects of the complex ageing process. Ageing can be considered the most prevalent pathophysiological condition in humans, affecting all tissue systems and acting as a driving force for many common and intractable disorders. The ageing process involves a complex interplay among various deleterious activities that profoundly disrupt the body's ability to cope with damage, thus increasing susceptibility to pathophysiologies such as neurodegeneration, central obesity, osteoporosis, type 2 diabetes mellitus and atherosclerosis. The biological systems that control ageing appear to function as a series of interconnected complex networks. The inter-communication among multiple lower-complexity signaling systems within the global ageing networks is likely coordinated internally by keystones or hubs, which regulate responses to dynamic molecular events through protein-protein interactions with multiple distinct partners. Multiple lines of research have suggested that GIT2 may act as one of these network coordinators in the ageing process. Identifying and targeting keystones, such as GIT2, is thus an important approach in our understanding of, and eventual ability to, medically ameliorate or interdict age-related progressive cellular and tissue damage.

Chemosensitizing effect of shRNA-mediated ERCC1 silencing on a Xuanwei lung adenocarcinoma cell line and its clinical significance

Lung cancer is a common fatal malignancy in both men and women. Xuanwei, Yunnan has the highest incidence of lung cancer in China. The area has a specific risk factor in the domestic combustion of bituminous coal, and lung cancer patients from this area tend to be resistant to platinum-based treatments. However, little is known about the mechanism of platinum resistance in patients from Xuanwei. Herein, we used lentiviral infection with shRNA to silence expression of the DNA repair enzyme ERCC1 in XWLC05 both in its RNA and protein expression level, a lung adenoma cell line derived from a patient from Xuanwei. ERCC1 expression in this cell line is high and contributes to its resistance to cisplatin. Suppression of ERCC1 decreased XWLC05 proliferation in vitro (IC50 of cisplatin 1.34 µM for shRNA-infected cells vs. 4.54 µM for control cells) and increased the apoptotic rate after treatment with cisplatin (81.2% shRNA cells vs. 58% control cells, P<0.05). Progression-free survival was longer in ERCC1-negative lung adenoma patients than those with high ERCC1 levels (30 vs. 11 months, P<0.0001). ERCC1 expression was identified as a prognostic marker for overall survival in the patient cohort with operable lesions. Taken together, our data identify ERCC1 as a disease marker in lung adenoma patients from Xuanwei and confirm the significance of resection for the subsequent effect of platinum treatment in these patients. Additional studies are needed to determine the mechanism of ERCC1-induced platinum resistance in lung adenoma patients from Xuanwei.

Combination gemcitabine/cisplatin therapy and ERCC1 expression for resected pancreatic adenocarcinoma: Results of a Phase II prospective trial

BACKGROUND

Standard adjuvant treatment for pancreatic adenocarcinoma (PDAC) is gemcitabine [Gem(CONKO-001: Gem vs. placebo DFS:13.4 vs. 6.7 mo; P < 0.001; OS:22.8 vs. 20.2 mo; P = 0.01)]. Addition of cisplatin (Cis) to Gem has resulted in increased PFS for advanced and metastatic disease, which may be predicted by low expression of excision repair cross-complementing group-1 (ERCC1), the key enzyme in nucleotide excision repair. This Phase II prospective trial assesses outcomes of patients treated with adjuvant Gem/Cis, stratifying results by tumor ERCC1 expression.

METHODS

Patients with resected PDAC were enrolled (2010-2013) and received Gem(1,000 mg/m(2) )/Cis(50 mg/m(2) ). Tumor ERCC1 expression was evaluated by immunohistochemistry and dichotomized into low or high expression. Primary outcomes were recurrence-free and overall survival (RFS/OS).

RESULTS

Of 22 pts, 16(73%) were Stage IIB, 5(23%) Stage IIA, and 1(4%) Stage IA. Grade 3/4 toxicity occurred in 13 pts (59%); neutropenia was most common (n = 9;41%). Median follow-up was 37.5 months. Median RFS was 16.7 mo; OS was 35.5 mo. Low ERCC1 (n = 15;75%) compared to high ERCC1 (n = 5;25%) was not associated with improved RFS (12.4 vs. 16.7 mo; P = 0.68) or OS (Median not reached vs. 21.6 mo; P = 0.22).

CONCLUSIONS

Adjuvant Gem/Cis is feasible in patients with resected pancreatic adenocarcinoma. RFS and OS for Gem/Cis appear promising compared to historic control. Tumor ERCC1 expression can be reliably evaluated, and low expression is present in most patients. J. Surg. Oncol. 2016;114:336-341. © 2016 Wiley Periodicals, Inc.

Prognostic value of excision repair cross-complementation group 1 expression in gastric cancer: A meta-analysis

The prognostic impact of excision repair cross-complementation group 1 (ERCC1) expression in gastric cancer (GC) has been investigated for decades, but has yielded controversial results. The aim of the present study was to provide a precise evaluation of whether the expression levels of ERCC1 are associated with overall survival (OS) in patients with GC. A systematic search of Medline and Embase was conducted. Original studies concerning OS and ERCC1 expression were included for critical appraisal. A total of 15 studies comprising 1,425 patients with GC were identified. The results revealed that high/positive ERCC1 expression was an indicator of poor survival in patients with GC [hazard ratio (HR) 1.48; 95% confidence interval (CI) 1.02–2.10; P=0.036; I²=83.8%; random-effects model] compared with low/negative ERCC1 expression. Subgroup analysis indicated that high/positive ERCC1 expression had a significant unfavorable impact on OS in the group of patients evaluated by reverse transcription polymerase chain reaction (RT-PCR; HR 2.57; 95% CI 1.49–4.45). Furthermore, high/positive ERCC1 expression was found to be associated with poor survival in patients receiving platinum-based chemotherapy in the RT-PCR group (HR 2.13; 95% CI 1.06–4.27). These data suggest that ERCC1 may be a useful prognostic factor for GC. In addition, low mRNA levels of ERCC1 appear to be associated with a significant favorable OS benefit from platinum-based chemotherapy.

Prognostic value of differential CCND1 expression in patients with resected gastric adenocarcinoma

Cyclin D1 (CCND1) plays essential roles in cancer progression. In this study, CCND1 expression patterns in 211 cases of resected gastric adenocarcinoma (RGA) tissue were determined by immunohistochemistry, and the association between CCND1 expression levels and RGA prognosis was analyzed. RGA tissues displayed differential CCND1 expression (high expression, 52.1 %; n = 110, and low expression, 47.9 %; n = 101). CCND1 expression levels were related with median overall survival time (MST). MST in patients with high CCND1 expression was 43 months, whereas with low CCND1 expression it was 62 months (P = 0.013). When data were stratified by postoperative treatments and CCND1 expression levels, the MST for patients treated with fluoropyrimidine plus platinum (n = 140) was significantly longer than for those treated with fluoropyrimidine only (n = 71) in both high and low CCND1 expression groups (65.0 vs. 29.0 months, P = 0.041; and 74.5 vs. 33.0 months, P = 0.003, respectively). Cox multivariate analyses further confirmed that high CCND1 expression was related with poor prognosis in both treatment groups [hazard ratio (HR) 1.91, 95 % confidence interval (CI) 1.12-3.23; P = 0.017, and HR 2.14, 95 % CI 1.08-4.25; P = 0.029] and that fluoropyrimidine plus platinum was more effective than fluoropyrimidine only in high CCND1 (HR 0.47, 95 % CI 0.28-0.78; P = 0.004) and low CCND1 (HR 0.44; 95 % CI 0.23-0.82; P = 0.01) expression patients. Therefore, CCND1 may be used as a prognostic biomarker for patients with RGA.

Predictive value of excision repair cross-complementation group 1 expression for platinum-based chemotherapy and survival in gastric cancer: a meta-analysis

PURPOSE

The predictive value of excision repair cross-complementation group 1 (ERCC1) gene for survival and response to platinum-based chemotherapy in gastric cancer (GC) remains controversial. We performed a meta-analysis to clarify the precise estimation of the prognostic and predictive effect of ERCC1.

METHODS

A systematic literature search was conducted using PubMed, ScienceDirect, Wiley and American Society of Clinical Oncology (ASCO) before March 2014. Studies analyzing survival data and/or chemotherapy response in GC by ERCC1 status were identified. The principal outcome measures were hazard ratios (HRs) for survival and relative risks (RRs) for chemotherapy response. Pooled HRs and RRs were calculated using fixed- or random-effects models according to the heterogeneity.

RESULTS

Twenty-one studies involving 1,628 patients met our inclusion criteria. High ERCC1 expression was significantly associated with shorter overall survival (OS) and lower response to chemotherapy in advanced GC patients receiving palliative chemotherapy (HR 1.83; 95 % CI 1.45-2.31; P < 0.001; RR 0.49; 95 % CI 0.38-0.62; P < 0.001). There was no significant difference in survival between high and low ERCC1 expression in adjuvant setting (OS: HR 1.38; 95 % CI 0.77-2.45; P = 0.276; EFS 0.72; 95 % CI 0.38-1.33; P = 0.291). Some evidence of heterogeneity and possible publication bias were discovered in few meta-analyses.

CONCLUSIONS

High ERCC1 expression might be an adverse prognostic and a drug-resistance predictive factor for advanced GC patients. However, further studies with consistent ERCC1 assessment methodology are needed.

How prognostic and predictive biomarkers are transforming our understanding and management of advanced gastric cancer

BACKGROUND

Gastric cancer (GC) is the second leading cause of cancer death worldwide. GC is a heterogeneous disease in terms of histology, anatomy, and epidemiology. There is also wide variability in how GC is treated in both the resectable and unresectable settings. Identification of prognostic and predictive biomarkers is critical to help direct and tailor therapy for this deadly disease.

METHODS

A literature search was done using Medline and MeSH terms for GC and predictive biomarkers and prognostic biomarkers. The search was limited to human subjects and the English language. There was no limit on dates. Published data and unpublished abstracts with clinical relevance were included.

RESULTS

Many potential prognostic and predictive biomarkers have been assessed for GC, some of which are becoming practice changing. This review is focused on clinically relevant biomarkers, including EGFR, HER2, various markers of angiogenesis, proto-oncogene MET, and the mammalian target of rapamycin.

CONCLUSION

GC is a deadly and heterogeneous disease for which biomarkers are beginning to change our understanding of prognosis and management. The recognition of predictive biomarkers, such as HER2 and vascular endothelial growth factor, has been an exciting development in the management of GC, validating the use of targeted drugs trastuzumab and ramucirumab. MET is another potential predictive marker that may be targeted in GC with drugs such as rilotumumab, foretinib, and crizotinib. Further identification and validation of prognostic and predictive biomarkers has the potential transform how this deadly disease is managed.

Correlation between expression of thymidylate synthase and clinical outcome of advanced gastric cancer treated with capecitabine alone chemotherapy

Thymidylate synthase (TS) is a prognostic marker in various tumors. However, the results of previous investigations in gastric cancer (GC) were controversial. The objective of this article is to investigate whether TS expression is associated with clinical outcome in advanced GC receiving capecitabine alone chemotherapy. The study reviewed 58 cases of advanced GC in patients aged ≥65 years between December 2008 and June 2012. All patients were treated with capecitabine alone chemotherapy. Immunohistochemical staining for TS protein expression was performed. The relationships between TS expression and clinicopathological characteristics (included age, gender, number of metastatic sites, Eastern Cooperative Oncology Group (ECOG) score, differentiation, and lymph node metastatic status), chemotherapy response, progression-free survival (PFS), and overall survival (OS) were evaluated. There was no association between TS expression and age, gender, number of metastatic sites, ECOG score, differentiation, and lymph node metastatic status (P > 0.05). The chemotherapy response rates among patients with low- and high-level expression of TS protein were 52.0 % (13/25) and 21.2 % (7/33), respectively (χ (2) = 5.968, P = 0.015). The median PFS and OS in patients with low-level TS expression were significantly longer than those with high-level TS expression (PFS 8.0 vs 2.8 m, P = 0.001; OS 13.3 vs 7.9 m, P = 0.002, respectively). Multivariate Cox regression analysis revealed that TS expression was independent risk factor for OS (hazard ratio (HR) 0.237; 95 % confidence interval (CI) 0.108 to 0.520; P = 0.000). The present study demonstrates that TS expression is associated with chemotherapy response, PFS, and OS in advanced GC patients treated with capecitabine alone chemotherapy.

Accurate detection of BRAF p.V600E mutations in challenging melanoma specimens requires stringent immunohistochemistry scoring criteria or sensitive molecular assays

Malignant melanoma patients require BRAF mutation testing prior to initiating BRAF inhibitor therapy. Molecular testing remains the diagnostic gold standard, but recent work suggests that BRAF immunohistochemistry (IHC) confers comparable results. Sample attributes and scoring criteria that may affect BRAF IHC interpretation, however, are poorly defined. We investigated formalin-fixed, paraffin-embedded samples with variable challenging interpretative attributes: metastases, core needle biopsies, sample tissues less than 60 mm(2), samples with greater than 50% necrosis, and/or samples with greater than 10% melanin pigmentation. Three pathologists independently scored 122 BRAF V600E IHC-labeled melanoma samples for percentage (0%-100%) of staining intensity (0-3+). Interscorer BRAF IHC discrepancies were resolved by consensus review. Lenient (≥1+, >0%) and stringent (≥2+, ≥10%) IHC scoring criteria were compared to BRAF V600 mutation (cobas) results (n = 118). Specimens with greater than 10% melanin pigmentation and metastatic samples produced the majority of interobserver IHC and IHC/cobas scoring discrepancies. Consensus review using stringent scoring criteria decreased the number of discrepant results, yielded very good interobserver reproducibility, and improved specificity and positive predictive value for BRAF p.V600E detection. BRAF p.V600K mutations accounted for 57.1% of false-negative IHC results when stringent, consensus criteria scoring were used. The cobas test detected 75.0% (8/12) of BRAF IHC-negative BRAF p.V600K mutations confirmed by next-generation sequencing. Molecular BRAF testing is the preferred screening test for BRAF inhibitor therapy eligibility because of superior sensitivity in challenging interpretative melanoma specimens. However, BRAF V600E IHC has excellent specificity and positive predictive value when stringent, consensus scoring criteria are implemented. To decrease IHC scoring discrepancies, pathologists should interpret metastatic and pigmented samples with caution.

Molecular profiling in gastric cancer: examining potential targets for chemotherapy

BACKGROUND AND OBJECTIVES

Current NCCN guidelines recommend epirubicin (E), cisplatin (C), and 5-fluorouracil (F) as a first-line therapeutic approach for operable gastric adenocarcinoma (GC). Molecular profiling (MP) was used to evaluate the expression of chemotherapy targeted biomarkers associated with ECF therapy and other first-line cytotoxic regimens for GC.

METHODS

GC specimens were analyzed by immunohistochemistry (IHC) for TOP2A, TS, ERCC1, PGP, and TOPO1 expression (Caris Life Sciences, Phoenix, AZ) from 2009 to 2012.

RESULTS

A total of 230 GC specimens were analyzed. The median age of patients was 61 (IQR: 50-72) years with the majority being male (n = 139, 60%). IHC actionable targets included: 60% (n = 138) high TOP2A, 55% (n = 127) negative ERCC1, and 63% (n = 145) negative TS, indicating potential benefit from E, C, and F, respectively. Simultaneous expression analysis demonstrated only 24% (n = 55) of patients had gene expression levels that suggested uniform sensitivity to ECF. Biomarker results of 6.5% (n = 15) of patients revealed a potential complete lack of sensitivity to first-line ECF.

CONCLUSIONS

MP of GC has the potential to define patients who would derive the greatest benefit from current therapies. Prospective controlled studies are required to validate the role of biomarkers in the management of GC patients.

ERCC1 mRNA expression as a postoperative prognostic marker in extrahepatic bile duct cancer

BACKGROUND

No reliable biomarker for biliary tract cancer has yet been identified because of the varying composition of the cancer type, differences in tumor location, a mixture of curative and non-curative operations, and differences in operative methods.

METHODS

Fifty extrahepatic bile duct cancer patients, pathologically diagnosed with papillary or tubular adenocarcinoma who underwent a pancreatoduodenectomy with R0 resection, were included in the study. Messenger RNA (mRNA) expression levels were measured from formalin-fixed, paraffin-embedded samples by real-time reverse-transcription polymerase chain reaction.

RESULTS

The preliminary analysis selected ten patients who have survived more than 5 years (LS group) and ten who had a relapse within 2 years (SS group). mRNA expression of seven target genes was examined, but only excision repair cross-complementing 1 (ERCC1) mRNA levels showed a significant difference between the LS and SS groups (median ERCC1: LS 26.5 vs. SS 9.7; p = 0.0073). The median survival time of patients with high ERCC1 levels was significantly longer than in patients with low ERCC1 levels (p = 0.0105). Thirty more patients with identical backgrounds were added to the study, and ERCC1 mRNA levels were measured in all 50 patients. Those with high ERCC1 mRNA levels had a significantly greater overall survival (OS) time compared with those with low ERCC1 levels (MST: 174 vs. 86 M; p = 0.048). Multivariate analysis found that an absence of lymph node metastases and high ERCC1 expression were significantly associated with improved OS.

CONCLUSION

ERCC1 mRNA expression appears to be a useful prognostic biomarker for extrahepatic bile duct cancer with R0 resection.

Targeting DNA damage response in cancer therapy

Cancer chemotherapy and radiotherapy are designed to kill cancer cells mostly by inducing DNA damage. DNA damage is normally recognized and repaired by the intrinsic DNA damage response machinery. If the damaged lesions are successfully repaired, the cells will survive. In order to specifically and effectively kill cancer cells by therapies that induce DNA damage, it is important to take advantage of specific abnormalities in the DNA damage response machinery that are present in cancer cells but not in normal cells. Such properties of cancer cells can provide biomarkers or targets for sensitization. For example, defects or upregulation of the specific pathways that recognize or repair specific types of DNA damage can serve as biomarkers of favorable or poor response to therapies that induce such types of DNA damage. Inhibition of a DNA damage response pathway may enhance the therapeutic effects in combination with the DNA-damaging agents. Moreover, it may also be useful as a monotherapy when it achieves synthetic lethality, in which inhibition of a complementary DNA damage response pathway selectively kills cancer cells that have a defect in a particular DNA repair pathway. The most striking application of this strategy is the treatment of cancers deficient in homologous recombination by poly(ADP-ribose) polymerase inhibitors. In this review, we describe the impact of targeting the cancer-specific aberrations in the DNA damage response by explaining how these treatment strategies are currently being evaluated in preclinical or clinical trials.