[Colorectal cancer: prognostic molecular markers]

Circulating free tumor DNA and colorectal cancer

Cancer is characterized by multiple somatic genetic and epigenetic alterations that could be useful as molecular markers for detecting tumor DNA in different bodily fluids. In patients with various diseases as well as in healthy subjects, circulating plasma and serum carry small amounts of non-cell-bound DNA. In this free circulating DNA, tumor-associated molecular alterations can be detected in patients who have cancer. In many instances, the alterations identified are the same as those found in the primary tumor tissue, thereby suggesting tumor origin from a fraction of the circulating free DNA. In fact, various types of DNA alterations described in colorectal cancer have been detected in the circulating free DNA of patients with colorectal cancer. These alterations include KRAS2, APC and TP53 mutations, DNA hypermethylation, microsatellite instability (MSI) and loss of heterozygosity (LOH). Also, advances in polymerase chain reaction (PCR)-based technology now allow the detection and quantification of extremely small amounts of tumor-derived circulating free DNA in colorectal cancer patients. The present report summarizes the literature available so far on the mechanisms of circulating free DNA, and on the studies aimed at assessing the clinical and biological significance of tumor-derived circulating free DNA in colorectal cancer patients. Thus, tumor-derived circulating free DNA could serve as a marker for the diagnosis, prognosis and early detection of recurrence, thereby significantly improving the monitoring of colorectal cancer patients.

Prognostic factors in node-negative colorectal cancer: a retrospective study from a prospective database

PURPOSE

There is a need to identify a subgroup of high-risk patients with node-negative colorectal cancer who have a poor long-term prognosis and may benefit from adjuvant therapies. The aim of this study was to evaluate the prognostic impact of clinical and pathological parameters in a retrospective study from a prospective, continuous database of homogenously treated patients.

METHODS

This study included 362 patients operated in a single institution for Dukes A and B (node-negative) colorectal cancer. The median follow-up was 140 months. The prognostic value of 13 clinical and pathological parameters was investigated.

RESULTS

Multivariate analysis identified six independent prognostic factors: age at time of diagnosis (hazard ratio (HR) = 1.076), number of lymph nodes removed (HR = 0.948), perineural invasion (HR = 2.173), venous invasion (HR = 1.959), lymphatic vessel invasion (HR = 2.126), and T4 stage (HR = 5.876).

CONCLUSION

These parameters could be useful in identifying patients with high-risk node-negative colorectal cancer who should be presented to adjuvant therapy.

Concordance of KRAS/BRAF Mutation Status in Metastatic Colorectal Cancer before and after Anti-EGFR Therapy

Anti-EGFR targeted therapy is a potent strategy in the treatment of metastatic colorectal cancer (mCRC) but activating mutations in the KRAS gene are associated with poor response to this treatment. Therefore, KRAS mutation analysis is employed in the selection of patients for EGFR-targeted therapy and various studies have shown a high concordance between the mutation status in primary CRC and corresponding metastases. However, although development of therapy related resistance occurs also in the context of novel drugs such as tyrosine kinase-inhibitors the effect of the anti-EGFR treatment on the KRAS/BRAF mutation status itself in recurrent mCRC has not yet been clarified. Therefore, we analyzed 21 mCRCs before/after anti-EGFR therapy and found a pre-/posttherapeutic concordance of the KRAS/BRAF mutation status in 20 of the 21 cases examined. In the one discordant case, further analyses revealed that a tumor mosaicism or multiple primary tumors were present, indicating that anti-EGFR therapy has no influence on KRAS/BRAF mutation status in mCRC. Moreover, as the preselection of patients with a KRAS(wt) genotype for anti-EGFR therapy has become a standard procedure, sample sets such ours might be the basis for future studies addressing the identification of potential anti-EGFR therapy induced genetic alterations apart from KRAS/BRAF mutations.