The molecular genetics of colorectal cancer

β-catenin and Her2/neu expression in rectal cancer: association with histomorphological response to neoadjuvant therapy and prognosis

BACKGROUND

Neoadjuvant treatment strategies have been developed to improve survival of patients with advanced rectal cancer. Since mainly patients with major histopathological response benefit from this therapy, predictive and prognostic markers are needed. We examined the association of β-catenin and Her2/neu protein expression with histopathologic response to neoadjuvant radiochemotherapy and prognosis in patients with locally advanced rectal cancer.

METHODS

Fifty-four patients (33 male; 21 female; median age 60.4 years) with locally advanced rectal cancer were included in this study. All patients received a neoadjuvant radiochemotherapy (50.4 Gy, 5-FU) followed by surgical resection. Histomorphologic regression was evaluated by Dworak and Cologne staging system. Major response was defined by Dworak classification when resected specimens contained less than 50% vital tumor cells (n = 14) and by Cologne grading system when resected specimens contained less than 10% vital tumor cells (n = 15). Intratumoral β-catenin (nuclear/membranous) and Her2/neu (cytoplasmatic/membranous) expression was determined by immunohistochemistry in pre- and post-therapeutic specimens and correlated with clinicopathologic parameters.

RESULTS

A significant association was detected between pre-therapeutic membranous β-catenin levels and response: patients with a lower β-catenin protein expression showed significantly more often a major response compared with patients having high intratumoral protein levels (p = 0.011). In addition, patients with a higher Her2/neu protein expression showed a significant survival benefit compared with patients having low intratumoral protein levels (5-year survival rate: 81% vs. low 41%; p = 0.023).

CONCLUSIONS

The pre-therapeutic β-catenin and Her2/neu protein expression seem to be valuable predictive and prognostic markers in the multimodality treatment of advanced rectal cancer.

Reprimo 824 G>C and p53R2 4696 C>G single nucleotide polymorphisms and colorectal cancer: a case-control disease association study

BACKGROUND

Improved survival from colorectal cancer (CRC) may result from screening for inherited genetic risk factors. Reprimo and p53R2 are p53-inducible genes involved in cell cycle surveillance and DNA repair. Single nucleotide polymorphisms (SNPs) of these genes have been discovered, but their effects on the genes' function and association with CRC is not known.

METHODS

Ninety healthy controls, 52 diverticular disease controls and 96 CRC cases were genotyped. DNA was extracted from buccal brush biopsies. Genotyping was performed by polymerase chain reaction (PCR) or polymerase chain reaction/restriction fragment length polymorphism (PCR/RFLP) methods. Tests for Hardy-Weinberg equilibrium and allelic- and genotype-disease association were performed online using the Finetti program.

RESULTS

All three populations were in Hardy-Weinberg equilibrium with respect to p53R2 4696C>G SNP, and no CRC associations were demonstrated with this SNP. The healthy and CRC populations were in Hardy-Weinberg equilibrium with respect to the Reprimo 824G>C SNP, but the diverticular disease population was not (P=0.03). No CRC were demonstrated with Reprimo 824G>C.

CONCLUSION

No association between p53R2 4696C>G and Reprimo 824G>C with CRC was shown by this study. An association between the Reprimo 824G>C heterozygote and diverticular disease may exist on the basis of deviation from Hardy-Weinberg equilibrium.

Emerging role of KLF4 in human gastrointestinal cancer

Recent analyses revealed that Krüppel-like factors (KLFs) play important roles in both normal development and carcinogenesis. Of the 16 known KLFs, KLF4 has been shown to be involved in the regulation of proliferation, differentiation and tumorigenesis of gastrointestinal tract epithelium. Clinical, experimental and mechanistic findings indicate that KLF4 is a bona fide tumor suppressor for both gastric and colorectal cancers. In this review, we summarize how this growing area of research has formed and the challenging new frontiers for better understanding of the oncogenic potential of the KLFs.

The I1307K APC mutation in a high-risk clinic setting: a follow-up study

While the I1307K APC mutation clearly confers an increased lifetime risk for colorectal cancer, there is a paucity of data on the natural history of colonic neoplasia in symptomatic and asymptomatic mutation carriers. In this study, 51 Jewish I1307K APC mutation carriers were identified in a high-risk familial cancer clinic over a 4-year period, of whom 29 (56.8%) (four males and 25 females) were successfully telephone interviewed for 0.5-5 years (mean 2.4 +/- 1.4) after initial genetic testing. Of these 29 cases, one individual was diagnosed with colon cancer at the age of 45 years, five had adenomatous polyps (mean number of polyps = 1.8), 11 had breast cancer (mean age at diagnosis 49.5 +/- 10.5 years), and 12 were asymptomatic, at the time of the testing. During the follow-up period, new colonic polyps were diagnosed in three mutation carriers, two with previously diagnosed colon cancer and polyps and only one of the asymptomatic mutation carriers, and two additional previously affected patients had new cancer diagnoses: gastric cancer and melanoma. From this descriptive study, it seems that the short-term risk for colonic polyps in I1307K APC mutation is low, primarily affecting patients with previously diagnosed colon tumors.

Identification of Krüppel-like factor 4 as a potential tumor suppressor gene in colorectal cancer

Krüppel-like factor 4 (KLF4 or GKLF) is an inhibitor of the cell cycle. The gene encoding KLF4 is localized on chromosome 9q, previously shown to exhibit allelic loss in colorectal cancer (CRC). In this study, we show that the mean level of KLF4 mRNA in a panel of 30 CRC was 52% that of paired normal colonic tissues. Similarly, the levels of KLF4 mRNA and protein in a panel of six established CRC cell lines were significantly lower than those of an untransformed colonic epithelial cell line. Using highly polymorphic DNA markers that flank the KLF4 locus, we found evidence for loss of heterozygosity (LOH) in two of eight surgically resected CRC specimens. In addition, LOH was observed in five of six CRC cell lines with one additional cell line exhibiting hemizygous deletion in the KLF4 gene. We also found that the 5'-untranslated region of KLF4 was hypermethylated in a subset of resected CRC specimens and cell lines. Lastly, the open-reading frame of KLF4 in two of three CRC cell lines examined contained several point mutations that resulted in a diminished ability to activate the p21(WAF1/Cip1) promoter. These findings indicate that KLF4 is a potential tumor suppressor gene in CRC.