Molecular gate keepers succumb to gene aberrations in colorectal cancer in Kashmiri population, revealing a high incidence area.

BACKGROUND/AIM: Colorectal cancer (CRC) is one of the leading malignancies worldwide and has been reported to show geographical variation in its incidence, even within areas of ethnic homogeneity. The aim of this study was to identify p53 and K-ras gene mutations in CRC patients in a Kashmiri population, and to assess whether these mutations are linked with clinicopathological parameters. MATERIALS AND METHODS: Paired tumor and normal tissue samples from a consecutive series of 53 patients undergoing resective surgery for CRC were prospectively studied for p53 and K-ras gene mutations by PCR/single strand conformation polymorphism (SSCP). RESULTS: Less than half (45%, 19/42) of the patients presented mutations in the p53 gene. Twenty eight mutations were found in the p53 gene, which comprised of 23 substitutions (17 transitions + 6 transversions), and five insertions. The 23 substitutions constituted 18 missense mutations, two nonsense mutations, and three silent mutations. Of the 28 mutations (7.14%) observed in this study, 2 were not previously reported for CRC samples and were identified as novel p53 mutations. A few patients (22.64%, 12/53) presented with mutations in K-ras, constituting 13 missense mutations, out of which 11 were G-->A transitions, one was a G-->C transversion, and one a G-->T transversion. More than half (61.5%) of the mutations occurred in codon 12 whereas a few (38.5%) occurred in codon 13. One tumor contained missense mutations in both codons. Comparison of the mutation profiles of our patients with those of other ethnic populations and regions reflected both differences and similarities, indicating co-exposure to a unique set of risk factors. CONCLUSION: Mutations of the p53 and K-ras genes are some of the most common genetic changes in the development of human CRC. The high frequency of p53 gene mutations implicates p53 as a predominant factor for CRC in the high-risk ethnic Kashmiri population.

Mutational spectrum of conserved regions of TP53 and PTEN genes in Kangri cancer (of the skin) in the Kashmiri population.

Kangri cancer is a unique, thermally induced squamous cell carcinoma (SCC) of the skin that develops due to persistent use of a Kangri (a brazier) by the Kashmiri people to combat the cold temperature during winter. Unlike classical UV-induced SCC of the skin, Kangri cancer appears on the legs and abdomen. Its common features are erythematous patches, recurrence and metastasis. In the absence of any molecular etiology, we made a preliminary attempt to estimate the nature and frequency of mutations in the TP53 and PTEN genes in Kangri cancer patients from Kashmir. PCR-SSCP analysis followed by direct sequencing revealed that TP53 mutations account for 40% (12/30) of sporadic Kangri cancer patients and that PTEN mutations account for only 6.6% (2/30). There were 16 mutations in TP53 exons 5 and 7, found in 12 patients. They consisted of 11 substitutions (7 transitions, 3 transversions and 1 double-base) and 5 insertions. The 11 substitutions represent 8 distinct missense mutations, 3 of which were silent mutations. The mutations detected in the PTEN gene consisted of one insertion and one C>T transition. This high percentage of TP53 mutations (especially A>G) showed a statistically significant association with age and positive lymph node status. Our results indicate that TP53 is a predominant target of chronic hyperthermia in the development of Kangri cancer in the moderate risk Kashmiri population. The differences in the TP53 mutation spectrum of UV-induced SCC of the skin and Kangri cancer are probably due to the nature of the respective environmental carcinogens. The study also suggests that TP53 may function as a potential molecular marker and prognostic tool, at least in a subset of sporadic Kangri tumors.