Background:

The WHO (2000) defines colorectal carcinoma (CRC) as a malignant epithelial tumor. Only tumors that penetrate the muscularis mucosa toward the serosa are considered invasive tumors. CRC is one of the leading causes of malignant neoplasms of the digestive tract. It affects men and women in similar proportions, with an average age of 62 years. Recent literature points to an increase in the incidence of this neoplasm in young patients. Molecularly, two major types of colon cancers can be distinguished. The first and most frequent type (85%) is associated with chromosomal instability by mutations in APC, Ras, and p53; while the other types are associated with the presence of microsatellite instability or alteration of specific DNA repair genes (8-12%). Mutations in K-Ras play a very important role in tumorigenesis; in the case of CRC, somatic mutations in K-ras are found in 25-40% of the cases. The mutation status of K-Ras is an important predictor marker for anti-epidermal growth factor receptor (EGFR) treatment because advanced or invasive CRC harboring K-Ras mutations appear to have a worse response to treatment than those with a non-mutated or wild-type (WT) genotype. Verifying the genotype before offering and initiating treatment with anti-EGFR drugs is of utmost importance.

Objective:

The aim of this study was to establish the mutation status of K-RAS in young Mexican patients with invasive CRC to determine possible candidates for anti-EGFR therapy in this age group and to know the clinical-pathological features in these cases.

Materials and methods:

Histological specimens of 23 cases of colectomies with CRC diagnosis were analyzed. A paraffin block from each case was submitted to a molecular study by real-time polymerase chain reaction to determine the mutation status of RAS (KRAS/NRAS).

Results:

In 14 cases (60.8%), KRAS/NRAS was not mutated with WT genotype; in four cases (17.3%), the samples could not be processed and the mutation status could not be determined; and in four cases (17.3%), mutations were found in KRAS.

Conclusions:

This descriptive study provides important statistical data that support CRC knowledge in the Mexican population, specifically on some clinical, histopathological, and mutational features of the Ras gene in young patients. Recent advances in molecular biology and the genetic classification of CRC are essential to individualize treatments and, in the coming years, to optimize them.

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