Clinicopathologic characteristics and gene expression analyses of non-KRAS 12/13, RAS-mutated metastatic colorectal cancer

BackgroundKRAS mutations in codons 12 and 13 are present in ∼40% of all colorectal cancers (CRC). Activating mutations in codons 61 and 146 of KRAS and in codons 12, 13, and 61 of NRAS also occur but are less frequent. The clinicopathologic features and gene expression profiles of this latter subpopulation of RAS-mutant colorectal tumors have not yet been clearly defined but in general are treated similarly to those with KRAS 12 or 13 mutations.Patients and methodsRecords of patients with metastatic CRC (mCRC) treated at MD Anderson Cancer Center between December 2000 and August 2012 were reviewed for RAS (KRAS or NRAS) and BRAF mutation status, clinical characteristics, and survival outcomes. To study further with an independent cohort, data from The Cancer Genome Atlas were analyzed to define a gene expression signature for patients whose tumors feature these atypical RAS mutations and explore differences with KRAS 12/13-mutated colorectal tumors.ResultsAmong the 484 patients reviewed, KRAS 12/13, KRAS 61/146, NRAS, and BRAF mutations were detected in 47.7%, 3.0%, 4.1%, and 7.4%, respectively, of patients who were tested for each of these aberrations. Lung metastases were more common in both the KRAS 12/13-mutated and atypical RAS-mutated cohorts relative to patients with RAS/BRAF wild-type tumors. Gene expression analyses revealed similar patterns regardless of the site of RAS mutation, and in silico functional algorithms predicted that KRAS and NRAS mutations in codons 12, 13, 61, and 146 alter the protein function and drive tumorgenesis.ConclusionsClinicopathologic characteristics, survival outcomes, functional impact, and gene expression profiling were similar between patients with KRAS 12/13 and those with NRAS or KRAS 61/146-mutated mCRC. These clinical and bioinformatic findings support the notion that colorectal tumors driven by these RAS mutations are phenotypically similar.     

Comparison of <Emphasis Type="Italic">KRAS</Emphasis> mutation status between primary tumor and metastasis in Chinese colorectal cancer patients

Detection of KRAS mutation status is a routine clinical procedure for predicting response to anti-EGFR therapy in colorectal cancer (CRC) patients. Previous studies showed high concordance of KRAS mutation status in primary lesion and corresponding metastatic sites in CRC. However, the data were mostly from Caucasians. The aim of this study is to compare KRAS mutation and other molecules mutation status between primary tumor and corresponding metastatic lesion in Chinese patients with CRC. In this retrospective study, Chinese CRC patients with paired samples of primary tumor and metastatic site were detected for KRAS codon 12 and 13 with quantitative real-time PCR, or detected for OncoCarta? panel of 19 genes with MassARRAY^® technique, including KRAS, BRAF, NRAS and PIK3CA et al. Forty-eight paired CRC samples were analyzed for KRAS codon 12 and 13 using quantitative real-time PCR. Ten paired samples were analyzed by 19 genes OncoCarta? Panel with MassARRAY^® technique. KRAS mutation was found in 15 (25.9 %) primary tumors and 18 (31.0 %) metastases. The discordance of KRAS was observed in 11 (19.0 %) patients. Alteration of mutation points in primary site with mutant KRAS was not observed. In the 10 patients with multiple gene detection, PIK3CA mutation showed concordant mutation status in primary tumor and metastatic site, whereas discordance in BRAF, NRAS and AKT1 was detected. A concordance rate of 81.0 % was detected in KRAS mutation between primary tumor and metastatic lesion in Chinese patients with CRC. Discordance of BRAF, NRAS and AKT1 mutation status in primary tumor and metastases was observed.     

CMS-dependent prognostic impact of KRAS and BRAFV600E mutations in primary colorectal cancer

BackgroundThe prognostic impact of KRAS and BRAF^V600E mutations in primary colorectal cancer (CRC) varies with microsatellite instability (MSI) status. The gene expression–based consensus molecular subtypes (CMSs) of CRC define molecularly and clinically distinct subgroups, and represent a novel stratification framework in biomarker analysis. We investigated the prognostic value of these mutations within the CMS groups.Patients and methodsTotally 1197 primary tumors from a Norwegian series of CRC stage I–IV were analyzed for MSI and mutation status in hotspots in KRAS (codons 12, 13 and 61) and BRAF (codon 600). A subset was analyzed for gene expression and confident CMS classification was obtained for 317 samples. This cohort was expanded with clinical and molecular data, including CMS classification, from 514 patients in the publically available dataset GSE39582. Gene expression signatures associated with KRAS and BRAF^V600E mutations were used to evaluate differential impact of mutations on gene expression among the CMS groups.ResultsBRAF^V600E and KRAS mutations were both associated with inferior 5-year overall survival (OS) exclusively in MSS tumors (BRAF^V600E mutation versus KRAS/BRAF wild-type: Hazard ratio (HR) 2.85, P < 0.001; KRAS mutation versus KRAS/BRAF wild-type: HR 1.30, P = 0.013). BRAF^V600E-mutated MSS tumors were strongly enriched and associated with metastatic disease in CMS1, leading to negative prognostic impact in this subtype (OS: BRAF^V600E mutation versus wild-type: HR 7.73, P = 0.001). In contrast, the poor prognosis of KRAS mutations was limited to MSS tumors with CMS2/CMS3 epithelial-like gene expression profiles (OS: KRAS mutation versus wild-type: HR 1.51, P = 0.011). The subtype-specific prognostic associations were substantiated by differential effects of BRAF^V600E and KRAS mutations on gene expression signatures according to the MSI status and CMS group.ConclusionsBRAF^V600E mutations are enriched and associated with metastatic disease in CMS1 MSS tumors, leading to poor prognosis in this subtype. KRAS mutations are associated with adverse outcome in epithelial (CMS2/CMS3) MSS tumors.     

Optimizing Single Agent Panitumumab Therapy in Pre-Treated Advanced Colorectal Cancer

PURPOSE: To improve the selection of advanced colorectal cancer patients to panitumumab by optimizing the assessment of RAS (KRAS-NRAS) mutations. EXPERIMENTAL DESIGN: Using a centralized pyrosequencing RAS assay, we analyzed the tumors of 94 patients, wild-type for KRAS mutations (codons 12 to 13) by Sanger sequencing (SS), treated with panitumumab. RESULTS: By SS analysis, 94 (62%) of 152 patients were wild-type and their objective response rate to panitumumab was 17%. We first optimized the KRAS test, by performing an accurate tissue-dissection step followed by pyrosequencing, a more sensitive method, and found further mutations in 12 (12.8%) cases. Secondly, tumors were subjected to RAS extension analysis (KRAS, exons 3 to 4; NRAS exons 2 to 4) by pyrosequencing that allowed to identify several rare mutations: KRAS codon 61, 5.3%; codon 146, 5.3%; NRAS, 9.5%. Overall, RAS mutation rate was 32.9%. All patients with additional RAS mutations had progressive or stable disease, except 3 patients with mutations at codon 61 of KRAS or NRAS who experienced partial (2 cases) or complete response. By excluding from the analysis 11 cases with mutations at codons 61, no patient was responsive to treatment (P = .021). RAS wild-type versus RAS mutated cases had a significantly better time to progression (P = .044), that resulted improved (p = .004) by excluding codon 61 mutations. CONCLUSION: This study shows that by optimizing the RAS test it is possible to significantly improve the identification of patients who do not gain benefit of panitumumab. Prospective studies are warranted to determine the clinical significance of rare mutations.     

Extended RAS testing in metastatic colorectal cancer—Refining the predictive molecular biomarkers

Mutations of exon 2 of Kirsten rat sarcoma viral oncogene homologue (KRAS) (exon 2 codons 12/13) lead to constitutive activation of the EGFR (epidermal growth factor receptor) mediated signal transduction pathway and been shown to be a negative predictive biomarker for EGFR-directed monoclonal antibodies among patients with colorectal cancer (CRC). As selection of patients is very important for administration of anti-EGFR therapy, this lone biomarker has proved to be insufficient for selecting the appropriate patients as more patients lacking exon 2 KRAS mutation were resistant to anti-EGFR therapy. The results of various randomized clinical trials have confirmed the presence of other RAS mutation including additional RAS mutations (KRAS exons 3/4 and NRAS exon 1/2/3/4). Extended RAS analysis should be considered before initiating anti-EGFR therapy to patients of metastatic CRC. This can help in proper selection of patients leading to tailored individualistic treatment, decreasing cost of treatment and the adverse effects related to use of monoclonal antibody therapy. The new evidence is supporting the need to make ‘Extended RAS’ analysis essential before start of treatment with anti-EGFR monoclonal antibody therapy. Prior to this the Extended RAS testing should be standardized.     

Role of NRAS mutations as prognostic and predictive markers in metastatic colorectal cancer

NRAS mutations occur in 3–5% of colorectal cancer. Differently from KRAS and BRAF mutations, the role of NRAS mutations as prognostic and predictive markers in metastatic colorectal cancer (mCRC) has been investigated to a lesser extent. A retrospective series suggested the role of NRAS mutations as predictors of resistance to anti‐EGFR monoclonal antibodies (MoAbs) in chemo‐refractory patients with mCRC. In our study, KRAS codons 12, 13, 61 and BRAF codon 600 mutational status were evaluated in mCRCs referred to our Institution from 2009 to 2012. NRAS codons 12, 13 and 61 mutational status was analyzed in KRAS/BRAF wt patients. We collected pathological and clinical features in the overall population and outcome data in a subset of NRAS mutated chemo‐refractory patients treated with anti‐EGFR MoAbs in advanced lines. NRAS was mutated in 47/786 (6%) mCRCs. NRAS and KRAS mutated tumors did not show significant differences in terms of clinical and pathological characteristics, except for a lower prevalence of mucinous histology (p = 0.012) and lung metastases (p = 0.012) among NRAS mutated tumors. In the uni‐ and multivariate model, NRAS mutations were associated with shorter overall survival (OS) compared to all wt patients (median OS 25.6 vs 42.7 months; univ: HR = 1.91, 95% CI 1.39–3.86, p = 0.0013; multiv: HR = 1.75, 95% CI 1.1.3–2.72, p = 0.013). None of the chemo‐refractory NRAS mutated patients evaluable for response to anti‐EGFRs achieved response. In conclusion, NRAS mutations have a relevant incidence in patients with mCRC and showed an association with specific clinical and pathological features. NRAS mutations affect mCRC patients' prognosis and predict lack of response to anti‐EGFRs.     

High Concordance and Negative Prognostic Impact of RAS/BRAF/PIK3CA Mutations in Multiple Resected Colorectal Liver Metastases

BackgroundThe prevalence and clinical implications of genetic heterogeneity in patients with multiple colorectal liver metastases remain largely unknown. In a prospective series of patients undergoing resection of colorectal liver metastases, the aim was to investigate the inter-metastatic and primary-to-metastatic heterogeneity of mutations in KRAS, NRAS, BRAF, and PIK3CA and their prognostic impact.Patients and MethodsWe analyzed the mutation status among 372 liver metastases and 78 primary tumors from 106 patients by methods used in clinical routine testing, by Sanger sequencing, by next-generation sequencing (NGS), and/or by droplet digital polymerase chain reaction. The 3-year cancer-specific survival (CSS) was analyzed using the Kaplan-Meier method.ResultsAlthough Sanger sequencing indicated inter-metastatic mutation heterogeneity in 14 of 97 patients (14%), almost all cases were refuted by high-sensitive NGS. Also, heterogeneity among metastatic deposits was concluded only for PIK3CA in 2 patients. Similarly, primary-to-metastatic heterogeneity was indicated in 8 of 78 patients (10%) using Sanger sequencing but for only 2 patients after NGS, showing the emergence of 1 KRAS and 1 PIK3CA mutation in the metastatic lesions. KRAS mutations were present in 53 of 106 patients (50%) and were associated with poorer 3-year CSS after liver resection (37% vs. 61% for KRAS wild-type; P = .004). Poor prognostic associations were found also for the combination of KRAS/NRAS/BRAF mutations compared with triple wild-type (P = .002).ConclusionIntra-patient mutation heterogeneity was virtually undetected, both between the primary tumor and the liver metastases and among the metastatic deposits. KRAS mutations separately, and KRAS/NRAS/BRAF mutations combined, were associated with poor patient survival after partial liver resection.     

KRAS codon 61, 146 and BRAF mutations predict resistance to cetuximab plus irinotecan in KRAS codon 12 and 13 wild-type metastatic colorectal cancer

Background:

KRAS codons 12 and 13 mutations predict resistance to anti-EGFR monoclonal antibodies (moAbs) in metastatic colorectal cancer. Also, BRAF V600E mutation has been associated with resistance. Additional KRAS mutations are described in CRC.

Methods:

We investigated the role of KRAS codons 61 and 146 and BRAF V600E mutations in predicting resistance to cetuximab plus irinotecan in a cohort of KRAS codons 12 and 13 wild-type patients.

Results:

Among 87 KRAS codons 12 and 13 wild-type patients, KRAS codons 61 and 146 were mutated in 7 and 1 case, respectively. None of mutated patients responded vs 22 of 68 wild type (P=0.096). Eleven patients were not evaluable. KRAS mutations were associated with shorter progression-free survival (PFS, HR: 0.46, P=0.028). None of 13 BRAF-mutated patients responded vs 24 of 74 BRAF wild type (P=0.016). BRAF mutation was associated with a trend towards shorter PFS (HR: 0.59, P=0.073). In the subgroup of BRAF wild-type patients, KRAS codons 61/146 mutations determined a lower response rate (0 vs 37%, P=0.047) and worse PFS (HR: 0.45, P=0.023). Patients bearing KRAS or BRAF mutations had poorer response rate (0 vs 37%, P=0.0005) and PFS (HR: 0.51, P=0.006) compared with KRAS and BRAF wild-type patients.

Conclusion:

Assessing KRAS codons 61/146 and BRAF V600E mutations might help optimising the selection of the candidate patients to receive anti-EGFR moAbs.     

Characterization of rare transforming KRAS mutations in sporadic colorectal cancer

KRAS mutational status has been shown to be a predictive biomarker of resistance to anti-EGFR monoclonal antibody (mAb) therapy in patients with metastatic colorectal cancer. We report the spectrum of KRAS mutation in 1506 patients with colorectal cancer and the identification and characterization of rare insertion mutations within the functional domain of KRAS. KRAS mutations are found in 44.5% (670/1506) of the patients. Two cases are found to harbor double mutations involving both codons 12 and 13. The frequencies of KRAS mutations at its codons 12, 13, 61, and 146 are 75.1%, 19.3%, 2.5%, and 2.7%, respectively. The most abundant mutation of codon 12 is G12D, followed by G12V and G12C while G13D is the predominant mutation in codon 13. Mutations in other codons are rare. The KRAS mutation rate is significantly higher in women (48%, 296/617) than in men (42.1%, 374/889, P = 0.023). Tumors on the right colon have a higher frequency of KRAS mutations than those on the left (57.3% vs. 40.4%, P < 0.0001). Two in-frame insertion mutations affect the phosphate-binding loop (codon 10–16) of KRAS are identified. One of them has never been reported before. Compared with wild-type protein, the insertion variants enhance the cellular accumulation of active RAS (RAS-GTP) and constitutively activate the downstream signaling pathway. NIH3T3 cells transfected with the insertion variants show enhanced anchorage-independent growth and in vivo tumorigenicity. Potentially these mutations contribute to primary resistance to anti-EGFR mAb therapy but the clinical implication requires further validation.     

Clinical Utility of KRAS and BRAF Mutations in a Cohort of Patients With Colorectal Neoplasms Submitted for Microsatellite Instability Testing

BackgroundMolecular analysis has become important in colorectal carcinoma (CRC) evaluation. Alterations in KRAS, BRAF, or mismatch repair (MMR) genes may determine therapeutic response or define a hereditary cancer syndrome. Correlation of DNA studies with clinical findings will further clarify the clinical utility of these markers.Patients and MethodsA retrospective study was performed on 111 paraffin-embedded tumor specimens submitted for microsatellite instability (MSI) testing based on clinical history or histologic examination, or both. DNA samples were screened for 7 KRAS mutations and the BRAF p.V600E mutation using fluorescent allele-specific polymerase-chain reaction (PCR) and capillary electrophoresis. Clinical data were collected through chart review.ResultsFifty-eight male and 53 female patients were studied. The incidence of KRAS and BRAF mutations was 49.5% and 7.2%, respectively. Dideoxy sequencing verified KRAS mutation status in 46 of 49 specimens tested. There was a trend toward significance of individual KRAS mutations on survival (P = .003). Dually positive KRAS and MSI tumors exclusively demonstrated p.G12D and p.G13D mutations (G>A transitions). BRAF-mutated tumors were predominantly right-sided and associated with a borderline worse prognosis. Forty-eight percent of tumors with MSI were present in the left colon or rectum.ConclusionAllele-specific PCR is an accurate and convenient method to assess KRAS and BRAF mutations and may detect mutations not identified by dideoxy sequencing. KRAS mutation status, in conjunction with morphologic or clinical parameters, may be useful in determining whether a tumor should be tested for MSI. MSI testing should not be considered exclusively in right-sided lesions. BRAF analysis may not be useful in rectal adenocarcinomas and should be evaluated in larger studies.     

Clinicopathologic features and prognostic value of KRAS,NRAS and BRAF mutations and DNA mismatch repair status: A single-center retrospective study of 1,834 Chinese patients with Stage I–IV colorectal cancer

Mutations of KRAS, NRAS, BRAF and DNA mismatch repair (MMR) status have become an important part of the assessment of patients with colorectal cancer (CRC), while respective clinicopathologic features and prognostic significance in specific stages and related detection strategies remain unclear. We retrospectively analyzed clinicopathologic features and prognosis of 1,834 patients with Stage I–IV colorectal adenocarcinoma. Mutations in KRAS, NRAS and BRAF and DNA MMR status were determined. The mutation rates of KRAS, NRAS and BRAF were 46.4, 3.2 and 3.5%, respectively, and the mismatch repair gene deletion (dMMR) rate was 5.6%. In a multivariate analysis, female, advanced age, tumor type histology, mucinous carcinoma and positive tumor deposits were associated with a high KRAS mutation rate. A high BRAF mutation rate was associated with female, poor differentiation, lymphovascular invasion and positive tumor deposits. Factors associated with high dMMR rates included low age, large tumor size, poor differentiation, Stages I–III. Tumor site was independently associated with KRAS mutation, BRAF mutation and dMMR. KRAS and BRAF mutations were independent risk factors for shorter overall survival (OS) in Stage IV tumors but not in Stage I–III tumors. NRAS mutation was an independent risk factor for shorter OS in Stage I–II tumors. dMMR was independently associated with longer OS in Stage III tumors.     

FOLFOX4 plus cetuximab treatment and RAS mutations in colorectal cancer

BackgroundThe OPUS study demonstrated that addition of cetuximab to 5-fluorouracil, folinic acid and oxaliplatin (FOLFOX4) significantly improved objective response and progression-free survival (PFS) in the first-line treatment of patients with KRAS exon 2 wild-type metastatic colorectal cancer (mCRC). In patients with KRAS exon 2 mutations, a detrimental effect was seen upon addition of cetuximab to FOLFOX4. The current study reports outcomes in subgroups defined by extended RAS testing.Patients and methodsSamples from OPUS study KRAS exon 2 wild-type tumours were reanalysed for other RAS mutations in four additional KRAS codons (exons 3–4) and six NRAS codons (exons 2–4) using BEAMing. A cutoff of ⩾5% mutant/wild-type sequences was selected to define RAS status; we also report an analysis using a cutoff based on the technical lower limit for mutation identification (0.1%).ResultsOther RAS mutations were detected in 31/118 (26%) evaluable patients. In the extended analysis of RAS wild-type tumours (n = 87), objective response was significantly improved by addition of cetuximab to FOLFOX4 (58% versus 29%; odds ratio 3.33 [95% confidence interval 1.36–8.17]; P = 0.0084); although limited by population size, there also appeared to be trends favouring the cetuximab arm in terms of PFS and overall survival in the RAS wild-type group compared with the RAS evaluable group. There was no evidence that patients with other RAS mutations benefited from cetuximab, but small numbers precluded precise estimations of treatment effects. In the combined population of patients with any RAS mutation (KRAS exon 2 or other RAS), a clear detrimental effect was associated with addition of cetuximab to FOLFOX4.ConclusionPatients with RAS-mutant mCRC, as defined by mutations in KRAS and NRAS exons 2–4, derive no benefit and may be harmed by the addition of cetuximab to FOLFOX4. Restricting cetuximab administration to patients with RAS wild-type tumours will further tailor therapy to maximise benefit.     

Panitumumab combined with irinotecan for patients with KRAS wild-type metastatic colorectal cancer refractory to standard chemotherapy: a GERCOR efficacy,tolerance, and translational molecular study

BackgroundThe purpose of this study was to evaluate the combination of panitumumab and irinotecan in patients with KRAS wild-type metastatic colorectal cancer refractory to standard chemotherapy (oxaliplatin, fluoropyrimidines–irinotecan and bevacizumab).Patients and methodsKRAS status was first determined locally but subsequent validation of KRAS status and additional screenings (rare KRAS, NRAS, BRAF mutations and EGFR copy number) were centrally assessed. Patients received panitumumab (6 mg/kg) and irinotecan (180 mg/m²) every 2 weeks.ResultsSixty-five eligible patients were analyzed. The objective response rate (ORR) was 29.2% [95% confidence interval (95% CI) 18.2–40.3]. Median progression-free and overall survivals were 5.5 and 9.7 months, respectively. Most frequent grade 3/4 toxic effects were skin 32.3%, diarrhea 15.4% and neutropenia 12.3%. Tissue samples were available for 60 patients. For the confirmed KRAS wild-type population codon 12 or 13 mutation (n = 54), ORR was 35.2% (95% CI 22.4.1–47.9). Thirteen patients had a NRAS, a BRAF or a rare KRAS mutation, and no tumor response was observed in this subgroup when compared with 46.3% (95% CI 31.1–61.6) ORR in the subgroup of 41 patients with no identified mutation.ConclusionPanitumumab and irinotecan is an active third-line regimen in a well-defined population based on biomarkers.ClinicalTrials.gov IdentifierNCT00655499.     

KRAS G12C Metastatic Colorectal Cancer: Specific Features of a New Emerging Target Population

BackgroundKirsten rat sarcoma viral oncogene (KRAS) G12C mutation occurs in about 4% of colorectal cancers (CRCs). Recently, KRAS G12C was identified to be a potential drug target and predictor of response to the novel on AMG510 target treatment. We described the clinicopathologic features and prognosis of KRAS G12C-mutated metastatic CRCs compared to other KRAS mutation.Patients and MethodsClinicopathologic features and outcome data of KRAS-mutated metastatic CRC (mCRC) patients referred to 3 Italian oncology units from January 2010 to December 2018 were collected. A cohort of KRAS-mutant mCRC patients referred to the Department of Medical Oncology at Fondazione IRCCS Istituto Nazionale dei Tumori, Milan (Italy) within the same time frame was included as external validation.ResultsA total of 839 KRAS-mutated mCRC cases were included in the main patient population. A total of 145 patients (17%) had KRAS G12C mutation. Our analyses showed that patients harboring KRAS G12C mutation were more likely to be men and to present lung and liver metastases, and were less likely to have peritoneal spread. KRAS G12C mutation was associated with shorter overall survival compared to other KRAS mutations (hazard ratio, 1.32; 95% confidence interval, 1.07-1.63; P = .009). Such results were confirmed in the external validation cohort.ConclusionThe knowledge of the distinctive traits of KRAS G12C-mutated CRC patients is crucial to future translational research studies, clinical trial design, and proper interpretation of results.     

Bevacizumab-based treatment in colorectal cancer with a NRAS Q61K mutation

Despite development of new therapies, metastatic colorectal cancer (mCRC) largely remains an incurable disease. Approximately 2–6 % of colorectal cancers harbor NRAS mutations. The anti-VEGF antibody bevacizumab is a backbone of most therapeutic regimens; however, biomarkers predicting its activity are not known. We report two cases of mCRC with a Q61K NRAS mutation that had a favorable response to bevacizumab and the histone deacetylase inhibitor valproic acid. In contrast, none of ten patients with wild-type NRAS or unknown NRAS status and mutated KRAS (NRAS and KRAS mutations are mutually exclusive) responded to the same regimen. These results suggest that NRAS mutation merits further investigation as a potential biomarker predicting the efficacy of bevacizumab-based treatment.     

Extended RAS mutations and anti-EGFR monoclonal antibody survival benefit in metastatic colorectal cancer: a meta-analysis of randomized,controlled trials

BackgroundMonoclonal antibodies (mAbs) targeting the epidermal growth factor receptor (EGFR) prolong survival in metastatic colorectal cancer (mCRC) Kirsten rat sarcoma viral oncogene (KRAS) exon 2 wild-type tumors. Recent evidence has suggested that other RAS mutations (in exons 3 and 4 of KRAS and exons 2, 3 and 4 of a related gene, NRAS) may also be predictive of resistance.MethodsSystematic review and meta-analysis of randomized, controlled trials (RCTs) evaluating anti-EGFR mAbs that have assessed tumors for new RAS mutations. Tumors with the new RAS mutations were compared with both tumors without any RAS mutations and tumors with KRAS exon 2 mutations with respect to anti-EGFR treatment progression-free survival (PFS) and overall survival (OS) benefit.ResultsNine RCTs comprising a total of 5948 participants evaluated for both KRAS exon 2 and new RAS mutations met the inclusion criteria. Approximately 20% of KRAS exon 2 wild-type tumors harbored one of the new RAS mutations. Tumors without any RAS mutations (either KRAS exon 2 or new RAS mutations) were found to have significantly superior anti-EGFR mAb PFS (P < 0.001) and OS (P = 0.008) treatment effect compared with tumors with any of the new RAS mutations. No difference in PFS or OS benefit was evident between tumors with KRAS exon 2 mutations and tumors with the new RAS mutations. Results were consistent between different anti-EGFR agents, lines of therapy and chemotherapy partners. Anti-EGFR mAb therapy significantly improved both PFS {hazard ratio 0.62 [95% confidence interval (CI) 0.50–0.76]} and OS [hazard ratio 0.87 (95% CI 0.77–0.99)] for tumors without any RAS mutations. No PFS or OS benefit was evident with use of anti-EGFR mAbs for tumors harboring any RAS mutation (P > 0.05).ConclusionTumors harboring one of the new RAS mutations are unlikely to significantly benefit from anti-EGFR mAb therapy in mCRC.     

Markers of resistance to anti-EGFR therapy in colorectal cancer

Epidermal growth factor receptor (EGFR) is a therapeutic target in colorectal cancer (CRC). The benefit from EGFR inhibitors appears to be limited to a subset of patients with CRC. Mechanisms of resistance to EGFR inhibitors are being identified. KRAS codon 12 activating mutation is a predominate mechanism of resistance to EGFR inhibitors in around 40% of patients with advanced CRC. Other potential mechanisms of resistance include ligand expression, increased EGFR number, mutations of BRAF and activation of alternate signaling pathways.Key Words: Resistance, anti-epidermal growth factor receptor (anti-EGFR), colorectal cancer     

KRAS and BRAF mutations in patients with rectal cancer treated with preoperative chemoradiotherapy

Background and purpose

KRAS and BRAF are mutated in 35% and 10% of colorectal cancers, respectively. However, data specifically for locally advanced rectal cancers are scarce, and the frequency of KRAS mutations in codons 61 and 146 remains to be established.

Materials and methods

DNA was isolated from pre-therapeutic biopsies of 94 patients who were treated within two phase-III clinical trials receiving preoperative chemoradiotherapy. Mutation status of KRAS exons 1-3 and BRAF exon 15 was established using the ABI PRISM Big Dye Sequencing Kit and subsequently correlated with clinical parameters.

Results

Overall, KRAS was mutated in 45 patients (48%). Twenty-nine mutations (64%) were located in codon 12, 10 mutations (22%) in codon 13, and 3 mutations (7%) in codons 61 and 146. No V600E BRAF mutation was detected. The presence of KRAS mutations was correlated neither with tumor response or lymph node status after preoperative chemoradiotherapy nor with overall survival or disease-free survival. When KRAS exon 1 mutations were separated based on the amino-acid exchange, we again failed to detect significant correlations (p = 0.052). However, G12V mutations appeared to be associated with higher rates of tumor regression than G13D mutations (p = 0.012).

Conclusion

We are the first to report the mutation status of KRAS and BRAF in pre-therapeutic biopsies from locally advanced rectal cancers. The high number of KRAS mutations in codons 61 and 146 emphasizes the importance to expand current mutation analyses, whereas BRAF mutations are not relevant for rectal carcinogenesis. Although the KRAS mutation status was not correlated with response, the subtle difference between G12V and G13D mutations warrants analysis of a larger patient population.     

Base excision repair-mediated resistance to cisplatin in KRAS(G12C) mutant NSCLC cells

KRAS mutations in NSCLC are supposed to indicate a poor prognosis and poor response to anticancer treatments but this feature lacks a mechanistic basis so far. In tumors, KRAS was found to be mutated mostly at codons 12 and 13 and a pool of mutations differing in the base alteration and the amino acid substitution have been described. The different KRAS mutations may differently impact on cancerogenesis and drug sensitivity. On this basis, we hypothesized that a different KRAS mutational status in NSCLC patients determines a different profile in the tumor response to treatments. In this paper, isogenic NSCLC cell clones expressing mutated forms of KRAS were used to determine the response to cisplatin, the main drug used in the clinic against NSCLC. Cells expressing the KRAS(G12C) mutation were found to be less sensitive to treatment both in vitro and in vivo. Systematic analysis of drug uptake, DNA adduct formation and DNA damage responses implicated in cisplatin adducts removal revealed that the KRAS(G12C) mutation might be particular because it stimulates Base Excision Repair to rapidly remove platinum from DNA even before the formation of cross-links.The presented results suggest a different pattern of sensitivity/resistance to cisplatin depending on the KRAS mutational status and these data might provide proof of principle for further investigations on the role of the KRAS status as a predictor of NSCLC response.