Efficacy of first-line systemic treatment in correlation with BRAF V600E and different KRAS mutations in metastatic colorectal cancer - a single institution retrospective analysis

BACKGROUND

KRAS mutation status in codons 12 and 13 is recognized as a predictive factor for resistance to anti-EGFR monoclonal antibodies. Despite having a wild type KRAS (wt-KRAS), not all patients with wt-KRAS respond to anti-EGFR antibody treatment. Additional mechanisms of resistance may activate mutations of the other main EGFR effectors pathway. Consequently, other molecular markers in colorectal cancer are needed to be evaluated to predict the response to therapy.

PATIENTS AND METHODS

In this retrospective study, objective responses (OR), time to progression (TTP), overall survival (OS) were analyzed in 176 metastatic colorectal cancer (mCRC) patients treated with first-line chemotherapy in combination with monoclonal antibodies in respect of KRAS status in codons 12 and 13 and BRAF mutational status.

RESULTS

The KRAS mutations were found in 63 patients (35.8 %), the KRAS mutation in codon 12 in 53 patients (30.1%) and the KRAS mutation in codon 13 in 10 patients (5.7%). The BRAF V600E mutation was detected in 13 of 176 patients (7.4%). In the subgroup of mCRC patients having wt-KRAS and wild type BRAF (wt-BRAF), the objective response rates were higher (OR 54.0% ,CR 14.7%, PR 39.3%) than in the patients with wt-KRAS and mt-BRAF (OR 38.5%,CR 15.4%, PR 23.1%), the difference was not statistically significant (p= 0.378). Median OS in patients with wt-KRAS wt-BRAF, and in patients with wt-KRAS mt-BRAF, was 107.4 months and 45 months, respectively. The difference was statistically significant (p= 0.042). TTP in patients with wt-KRAS wt-BRAF, and in patients with wt-KRAS mt-BRAF, was 16 months and 12 months, respectively. The difference was not statistically significant (p= 0.558).

CONCLUSIONS

Patients with BRAF V600E mutation have statistically significantly worse prognosis than the patients with wt-BRAF and progress earlier during treatment. The definitive role of the BRAF V600E mutation as a prognostic and predictive factor for the response to anti-EGFR monoclonal antibodies needs to be analyzed in large prospective clinical studies.

Neuroendocrine and squamous colonic composite carcinoma: Case report with molecular analysis

Composite colorectal carcinomas are rare. There are a modest number of cases in the medical literature, with even fewer cases describing composite carcinoma with neuroendocrine and squamous components. There are to our knowledge no reports of composite carcinoma molecular alterations. We present a case of composite carcinoma of the splenic flexure in a 33 year-old Caucasian male to investigate the presence and prognostic significance of molecular alterations in rare colonic carcinoma subtypes. Formalin-fixed paraffin-embedded (FFPE) tissue was hematoxylin and eosin- and mucicarmine-stained according to protocol, and immuno-stained with cytokeratin (CK)7, CK20, CDX2, AE1/AE3, chromogranin-A and synaptophysin. DNA was extracted from FFPE tissues and molecular analyses were performed according to lab-developed methods, followed by capillary electrophoresis. Hematoxylin and eosin staining showed admixed neuroendocrine and keratinized squamous cells. Positive nuclear CDX2 expression confirmed intestinal derivation. CK7 and CK20 were negative. Neuroendocrine cells stained positively for synaptophysin and AE1/AE3 and negatively for chromogranin and mucicarmine. Hepatic metastases showed a similar immunohistochemical profile. Molecular analysis revealed a G13D KRAS mutation. BRAF mutational testing was negative and microsatellite instability was not detected. The patient had rapid disease progression on chemotherapy and died 60 d after presentation. Although the G13D KRAS mutation normally predicts an intermediate outcome, the aggressive tumor behavior suggests other modifying factors in rare types of colonic carcinomas.

Efficacy of the monoclonal antibody EGFR inhibitors for the treatment of metastatic colorectal cancer

Two anti-epidermal growth factor receptor (EGFR) monoclonal antibodies (MoAbs) have been approved in Canada for the treatment of metastatic colorectal cancer (mCRC) – cetuximab, a mouse-human chimeric MoAb, and panitumumab, a fully human MoAb. This paper reviews the efficacy of the anti-EGFR monoclonal antibodies cetuximab and panitumumab – both as monotherapy and in combination with cytotoxic chemotherapy – in the treatment of mCRC. Both cetuximab and panitumumab have demonstrated clinical efficacy in monotherapy in patients with mCRC, an advantage that has recently been found to be limited largely to those with wild-type KRAS tumors. Advantages of using these agents in monotherapy include reduced cost and toxicity. While the addition of cetuximab to irinotecan has shown superior progression-free survival and response compared with cetuximab monotherapy, there is currently no evidence for a benefit of panitumumab in combination with irinotecan.

Systematic review of pharmacogenetic testing for predicting clinical benefit to anti-EGFR therapy in metastatic colorectal cancer

Pharmacogenetic testing can help identify patients with metastatic colorectal cancer more likely to respond to anti-EGFR therapy. We systematically reviewed the benefits and harms of EGFR-related pharmacogenetic testing of molecular targets downstream to KRAS in the treatment of metastatic colorectal cancer. We searched five electronic databases from January 2000 through November 2010, and conducted separate grey literature and conference abstracts searches. Two reviewers independently assessed all articles for relevance and quality. We identified 27 studies, primarily fair- to marginal-quality, small retrospective, and single-arm cohort studies with significant overlap in patient populations. We identified seven studies that studied BRAF in independent patient populations, one that studied NRAS, four that studied PIK3CA, eight that studied PTEN expression, and five that studied AKT expression. The best evidence for BRAF, NRAS, and PIK3CA comes from the largest retrospective study (n=649) of chemorefractory patients from seven European countries. In this study, BRAF mutation was present in 6.5% of KRAS wild-type tumors. Only 8.3% of persons with BRAF mutations, compared to 38% of persons without BRAF mutations (p=0.0012), responded to chemotherapy with cetuximab. Clinical sensitivity and the false positive fraction (1- specificity) were estimated at 9.8% (95% CI 6.3, 14.5) and 1.6% (95% CI 0.2, 5.6), respectively. BRAF mutation was also associated with worse median progression-free survival (absolute difference 18 weeks, p<0.0001), and overall survival (absolute difference 28 weeks, p<0.0001). In the only study comparing outcomes in persons who did (n=227) and did not (n=332) receive cetuximab with combination chemotherapy, those with BRAF mutation had worse survival outcomes regardless of whether or not they received cetuximab. Although NRAS and PIK3CA exon 20 mutations were also associated with worse outcomes compared to persons without these mutations, evidence is based on a small number of identified mutations. Evidence for protein expression of PTEN and AKT is more sparse and limited by variable methods for assessing protein expression. Low-quality evidence addressing clinical validity of pharmacogenetic testing in metastatic colorectal cancer patients suggests that BRAF mutations are associated with poorer treatment response and survival outcomes, although this association may be independent of treatment with EGFR inhibitors.

Mechanisms of aneuploidy induction by RAS and RAF oncogenes

Most cancers progress with the accumulation of genetic mutations with time and this is frequently associated with the acquisition of genomic instability in the form of whole chromosome changes, chromosomal rearrangements, gene amplifications or smaller changes at the nucleotide level. Whole chromosome instability (W-CIN), characterised by aneuploidy, is a major form of genomic instability observed in human cancers and several lines of evidence now support the argument that W-CIN is a promoter of tumourigenesis rather than being a passenger event. The primary mechanism proposed for evolution of CIN is abnormalities in mitosis/cytokinesis. However, mutations in genes directly involved in controlling mitosis/cytokinesis are rare in human cancers and so the mechanisms underpinning the evolution of CIN in cancers are not currently clear. On the other hand, mutations in RAS or BRAF are frequently found in human cancers, many of which demonstrate CIN, suggesting a possible link between deregulated signaling through the RAS/RAF/MEK/ERK pathway and CIN. In this review, we focus on a potential relationship between deregulated RAS/RAF signaling and CIN, and discuss possible mechanisms connecting the two.

Novel targeted therapies for the treatment of metastatic melanoma

The National Comprehensive Cancer Network guidelines for the treatment of stage IV metastatic melanoma state that clinical trials should be the preferred treatment option for these patients; therefore, clinical trials for these patients are the "standard of care." Our greater understanding of the molecular biology behind the development of melanoma has guided much of the translational research in this disease and has led to the development of novel targeted therapies. Specifically, advancement in our knowledge of alterations in signal transduction pathways in melanoma has led to the rapid development of a number of pharmacologic agents that inhibit these pathways. This review will discuss changes in signal transduction pathways involved in melanoma, specifically, activated mitogen-activated protein kinase, activated PI3 kinase, and inactivated p53/Rb pathways. This article will also review new targeted therapy in the context of the molecular biology of melanoma.

BRAFV600E mutation in papillary thyroid carcinoma: a potential target for therapy?

This article reviews the therapeutic significance of the close genotype-phenotype association in papillary thyroid carcinoma, namely regarding the association between genetic alterations in RET, BRAF or RAS genes and the histopathological variants of papillary thyroid carcinoma. Based upon the aforementioned review on morphology and molecular pathology, the most recent prognostic and therapeutic data are reviewed and the role of targeted therapies, namely those interfering with BRAF-activated pathways are discussed, which may play a role in the treatment of patients with papillary thyroid carcinoma unresponsive to radioactive iodine.

Molecular determination of benign and malignant thyroid tumors

Recent molecular studies have revolutionized our understanding of the pathogenesis of thyroid tumors and particular advances have been made in three areas. First, toxic thyroid nodules, which originate from constitutive activation of thyroid-stimulating hormone receptor/Gs α signaling and represent the dominant cause of thyrotoxicosis in regions with iodine deficiency. Second, papillary thyroid cancer, the most frequent thyroid malignancy, which is characterized by a common fingerprint of constitutive mitogen-activated protein kinase activation. Importantly, this is caused by distinct genetic alterations in radiation-induced (RET/PTC, NTRK and AKAP9/BRAF rearrangements) and sporadic tumors (BRAF and RAS point mutation) and, recently, there exciting in vitro have emerged explaining the structural basis for this. These findings suggest a scenario in which the fate of a thyroid tumor is determined by the specific genetic defect at the beginning. Third, application of microarray analysis in nodular pathologies in which the oncogenic pathway is less clear, notably follicular neoplasia, has led to the identification of a number of promising genetic markers (TFF-3, Gal-3, PLAB, CCND2 and PCKD2) for the diagnostic distinction of follicular adenoma and carcinoma. In addition to the diagnostic perspective, the identification of molecular fingerprints of thyroid tumors opens novel avenues for an improved therapeutic approach; for example, selective antagonism of cell signaling in treatment-refractory thyroid cancer.

BRAF, K-ras and BAT26 mutations in colorectal polyps and stool

AIM: To assess the feasibility of using BRAF, K-ras and BAT26 genes as stool-based molecular markers for detection of colorectal adenomas and hyperplastic polyps (HPs).

METHODS: We applied PCR-SSCP and direct sequencing to detect BRAF mutations of polyps and paired stool samples. Primer-mediated restriction fragment length polymorphism (RFLP) analysis and mutant-enriched PCR were used in detection of K-ras mutations of polyp tissues and paired stool samples respectively. BAT26, a microsatellite instability marker was examined by detection of small unstable alleles in a poly (A) repeat.

RESULTS: No genetic alterations were detected in the 36 colonoscopically normal patients in either tissues or stools. BRAF, K-ras and BAT26 mutations were found in 4 (16%), 10 (40%) and 3 (12%) of 25 adenoma tissues and among them, 75%, 80% and 100% of patients were observed to contain the same mutations in their corresponding stool samples. In HPs, mutations of BRAF and K-ras were detected in the tumor DNA of 2 (11.1%) and 8 (33.3%) of 18 patients respectively, all of whom had identical alterations in their stools. Taken together, the three genetic markers detected 15 (60%) of 25 adenomas and 8 (44.4%) of 18 HPs. The sensitivity of stool detection was 80% for adenomas and 100% for HPs with an overall specificity of 92% for adenomas and 100% for HPs.

CONCLUSION: BRAF, K-ras and BAT26 genes have the potential to be molecular markers for colorectal adenomas and HPs, and can be used as non-invasive screening markers for colorectal polyps.