Prognostic value of p53 overexpression and c-Ki-ras gene mutations in colorectal cancer

Genetic aspects of colorectal cancer: the surgeon's view

A characteristic feature of colorectal cancer genesis is its stepwise progression, which offers unique possibilities for studying its development. There are two principal kinds of mutation leading to uncontrolled cell proliferation and cancer. The first renders a stimulatory gene hyperactive--generation of an oncogene--and the second is the inactivation of a tumour suppressor gene. Current knowledge suggest that the change from normal mucosa to a small adenoma may be mediated by mutations of the APC gene and MCC gene on chromosome 5, by chromosome 5 deletion, by c-myc activation, and by DNA hypomethylation. The development to a large adenoma may be caused by Ki-ras mutation and further change to a dysplastic adenoma by deletion of the DCC gene on chromosome 18. The ability to become an invasive carcinoma may then be mediated by p53 mutations and deletion of chromosome 17p. Identification of genetic markers for metastatic disease is under progress.

Prognostic value of TP53 and K-ras-2 mutational analysis in stage III carcinoma of the colon

BACKGROUND

Genetic mutations involving oncogenes and tumor-suppressor genes occur in carcinogenesis, and may affect biologic behavior of neoplasms. In this study, we analyzed the prognostic value of mutational analysis in colon carcinoma.

PATIENTS AND METHODS

Archival pathology specimens from 70 consecutive patients, resected for stage III colon carcinoma, were analyzed for point mutations by amplification and direct sequencing of exons from the K-ras-2 and the TP53 genes (topographic genotyping). Mutations were compared with adverse histopathologic features (poor differentiation, vascular and lymphatic invasion, mucin production) as prognostic markers.

RESULTS

Five-year survival was 75% in patients with nonmutated lesions, significantly lower (21%) with TP53 mutations (P = 0.01), and intermediate with K-ras-2 only (45%) or both K-ras-2 and TP53 mutations (36%). A TP53 mutation carried the highest relative risk of death (2.39; 95% confidence interval, 1.29 to 4.42; P = 0.006). There was an additive effect on the risk of death between TP53 mutations and adverse histopathologic features.

CONCLUSIONS

The information derived from mutational analysis is creating new prognostic variables that may play a role in the choice of therapy for colorectal carcinoma.

Prediction of recurrence in B-C stages of colorectal cancer by p53 nuclear overexpression in comparison with standard pathological features

This study investigated the predictive value of p53 nuclear overexpression on recurrence of colorectal adenocarcinomas compared with established prognostic pathological features. Sixty-one paraffin-embedded sections from primary tumours were examined by immunohistochemistry. Specific nuclear staining was detected in 27 (44.2%) cases. Positivity was more frequent in tumours with venous invasion (76.9%) (P = 0.06) and in rectal cancer (68.4%) (P = 0.06). After a median observation time of 46 months, p53-positive tumours exhibited a higher percentage of recurrence (40.7% vs 11.7%) (P = 0.03), and a higher likelihood of relapse at 5-year follow-up (46% vs 13%) (P = 0.006). Among the pathological variables analysed, only the extent of bowel wall invasion showed a relationship with recurrence. After adjustment for the other covariates in a Cox's regression model, p53 overexpression was the only factor showing independent prognostic significance (hazard ratio: 4.96; 95% Confidence Interval (CI): 1.47-16.71) (P = 0.012). The results of this study show that nuclear p53 protein overexpression has higher predictive value than standard pathological variables.

p53 nuclear overexpression may not be an independent prognostic marker in early colorectal cancer

PURPOSE

This study was designed to determine if p53 nuclear overexpression, as detected by immunohistochemistry, is a marker of prognostic significance in early (Stage I) colorectal cancer (CRC).

METHODS

Tissue sections obtained from archival blocks of 66 patients with surgically treated Stage 1 CRC were stained immunohistochemically for p53 using a monoclonal antibody (PAB 1801-Ab2). Differences in survival between p53 positive (p53+) and p53 negative (p53-) groups were compared using Kaplan-Meier survival curves and the log-rank test.

RESULTS

Thirty-four patients (51.5 percent) were p53+ and 32 (48.5 percent) were p53-. There were significantly more p53+ tumors in females (23 of 34) compared with males (11 of 34) (P = 0.01). Follow-up ranged from 1 to 128.5 (mean, 44.7; median, 38.2) months. Thirteen patients (19.7 percent) developed recurrence, of whom five died of disease. Univariate analysis of clinical and pathologic variables did not reveal my statistically significant differences between p53+ and p53- tumors. Mean actuarial survival was longer (48.2 months) in the p53- group compared with the p53+ group (41.5 months). However, comparison of survival curves using the log-rank test did not show a statistically significant difference in survival (log-rank chi-squared = 0.2; P = 0.6).

CONCLUSION

p53 nuclear overexpression does not appear to be an independent marker of prognostic significance in surgically treated early CRC. Females were more likely to have p53+ tumors. The biologic significance of this findings is unknown.

The relationship of p53 expression to the prognosis of 418 patients with gastric carcinoma

BACKGROUND

Mutations of the p53 gene belong to the most common genetic alterations in human cancer that have been implicated in tumorigenesis and tumor progression. Although p53 expression appears to be correlated with prognosis in patients with breast cancer and some other types of cancer, its prognostic role in gastric cancer is still uncertain. In the present study, therefore, the prognostic impact of p53 expression was evaluated in 418 patients with curatively resected gastric carcinomas without residual tumor (RO-resection).

METHODS

Tumor sections of 418 RO-resected gastric carcinomas were stained with the monoclonal antibody DO-1 after microwave processing. p53 expression was statistically compared with clinico-pathologic features and postoperative survival.

RESULTS

p53 expression was detected in 57.5% of all tumors, with strong inter- and intratumor heterogeneity. No immunoreactivity was observed in the normal mucosa adjacent to the tumor. Statistically, no significant correlation between p53 overexpression and depth of invasion, lymph node involvement, or grade of tumor differentiation was detected. The correlations with blood vessel invasion (P = 0.049) and lymphatic vessel invasion (P = 0.047) were of marginal significance. Survival analysis revealed no significant impact of p53 expression on survival, the 5-year survival rates were 40.6% +/- 7.8% for patients with p53 positive tumors and 49.2% +/- 8.9% for patients with p53 negative tumors (P = 0.43). Furthermore, no correlation with survival was found when four different levels of p53 expression were analyzed (P = 0.51). p53 expression had no influence on survival, in either the lymph node positive or negative groups.

CONCLUSIONS

The data suggest that the immunohistochemical detection of p53 expression is at present not a predictor of outcome of patients with gastric cancer or to identify subgroups of patients who may be at higher risk.

Role of adjuvant therapy in surgically resected colorectal carcinoma

An important advance in cancer treatment has been made in recent years with the finding that adjuvant therapy can significantly improve the survival of patients with colorectal cancer. In patients with resected lymph node-positive colon carcinomas (TNM stage 3), adjuvant 5-fluorouracil and levamisole produced an unequivocal survival advantage that established this combination as the standard of clinical practice. Given that biochemical modulation of fluorouracil by leucovorin can increase response rates in advanced disease, this combination is undergoing evaluation as an adjuvant treatment. Preliminary results indicate that 5-fluorouracil and leucovorin are effective in reducing disease relapse; however, the effect of this regimen on patient survival rates awaits extended follow-up. In the treatment of stages 2 and 3 rectal cancer, significant reductions in local recurrence and death rates have been achieved with the combination of 5-fluorouracil and radiation therapy. Immunologic approaches and newer chemotherapeutic agents may further improve patient outcome and are under investigation, as are efforts to reduce the toxic effects of cancer chemotherapy. Increased understanding of the biology of these diseases is likely to yield prognostic markers capable of identifying subgroups of earlier stage patients at high risk of disease relapse who may also benefit from adjuvant therapy.

Prognostic value of pathological characteristics of colorectal cancer

The overall cure rate of colon cancer has not improved dramatically in the last decade, remaining at approximately 60% 5-year survival. The main reason for this lack of progress is that at the moment the primary tumour is resected, a significant proportion of the patients with seemingly localised disease already has (undetectable) micrometastases, mostly in the liver. The most important prognostic indicators have been extension of the tumour into the bowel wall and the presence of lymph node metastasis, as expressed in the Dukes classification. However, in the Dukes B and C categories, these parameters are poor predictors of final outcome. For improvement of the prognosis, in addition to earlier detection, more aggressive (adjuvant) treatment of high risk patients would be a rational strategy. This requires development of new therapeutic modalities, but also reliable stratification of patients according to high risk or low risk for recurrent disease. In recent years, many attempts have been made to improve the prediction of final outcome. Parameters studied include inflammatory response to the primary tumour, tumour cell growth fraction, tumour cell differentiation, genetic abnormalities and expression of genes involved in invasion and metastasis. Although some of these newer parameters have significant predictive value, in multivariant analyses, most appear to have limited independent value. Recent studies indicate that genetic abnormalities might be important new prognostic indicators. One of the most promising findings in this area is an allelic loss of chromosome 18q, which allows division of Dukes B patients into subgroups with low risk and high risk for recurrent disease.

Detection of loss of heterozygosity in the p53 tumor suppressor gene using a PCR-based assay

Inactivation of the p53 tumor suppressor gene has been reported to be a prognostic factor in several human cancer types. Normal function of the gene is affected by deletion in one allele; dysfunction of the other allele is often caused by a mutation. In tumors of heterozygous individuals, deletion of one allele can be detected as loss of heterozygosity (LOH). A recently found variable number of tandem repeats (VNTR) segment in intron 1 of the p53 gene seems to be highly polymorphic and, therefore, a very useful marker in detecting LOH in various types of tumor samples. We in vitro amplified the VNTR segment from genomic DNA samples of 101 lung cancer patients and run conventional agarose gel electrophoreses in order to detect the alleles of various length, differing by the number of repeats. The usefulness of the method was studied using DNA from white blood cell samples and from fresh and formalin-fixed, paraffin-embedded tumor samples. Of the patients, 56% were found to have two different alleles, i.e. were informative in this assay. In 18% of the lung tumors from the informative cases, LOH in the p53 suppressor gene was detected.

Evaluation of p53 protein expression as a marker for long-term prognosis in colorectal carcinoma

Mutation of the p53 gene is reported to be of prognostic importance in colorectal carcinomas. Immunohistochemical staining of the accumulated p53 gene product may be a simple alternative for p53 mutation analysis. Previous studies addressing the prognostic importance of p53 expression, however, yielded contradictory results. Therefore, we evaluated the importance of p53 expression as a marker for long-term prognosis in a well-characterised study population of 109 colorectal carcinomas. After antigen retrieval with target unmasking fluid (TUF), immunostaining of p53 was performed with both monoclonal antibody DO7 and polyclonal antibody CM1. Objective quantification of the p53 signal was assessed by a computerised image analyser. p53 expression was higher in non-mucinous tumours than in mucinous tumours (p53 labelling index = 30% and 17% respectively, P = 0.05), and in metastatic tumours compared with non-metastatic tumours (p53 labelling index = 37% and 22% respectively, P = 0.05). Other histopathological features were not related to p53 expression. In multivariate analysis, Dukes' stage (P = 0.02) and histological grade (P = 0.05) stood out as independent markers for prognosis. p53 expression was not an independent marker for prognosis. At present, p53 expression is not a useful marker for long-term prognosis. Further insight into the relationship between p53 mutations and p53 expression is needed to elucidate more precisely the clinical relevance of p53 alterations.

DNA ploidy and proliferating cell nuclear antigen in colonic adenomas and adenocarcinomas

To investigate the colonic adenoma-adenocarcinoma progression sequence, DNA ploidy analysis was performed on hyperplastic polyps to adenocarcinomas. DNA ploidy data were then compared with immunocytochemical staining for proliferating cell nuclear antigen (PCNA). In hyperplastic polyps to villous adenomas, all cases were diploid except one aneuploid villous adenoma. In three adenomas, diploid in situ adenocarcinomas were present. As diploid percentages decreased from hyperplastic polyps to villous adenomas, aneuploid percentages increased. In adenocarcinomas, the Dukes classification corresponded well to DNA ploidy status: all four stage A carcinomas were diploid, whereas three cases each of stage C1 and C2 carcinomas were aneuploid or multiploid. A surprising finding was that S-phase percentage in adenocarcinomas was not parallel with PCNA-positive tumor cell numbers. It is concluded that multistep adenoma-adenocarcinoma progression was partially reflected in DNA ploidy pattern from hyperplastic polyps to villous adenomas. In adenocarcinomas, the Dukes classification paralleled well the DNA ploidy status from stage A diploid to stage D aneuploid, but was not accompanied by increasing PCNA-positive cell numbers.

Cyclin/proliferation cell nuclear antigen immunohistochemistry does not improve the prognostic power of Dukes' or Jass' classifications for colorectal cancer

Immunohistochemistry of cyclin/proliferation cell nuclear antigen (PCNA) is an attractive alternative to tumour cell proliferation activity determined by flow cytometry which has been shown to be independently predictive of survival in patients with colorectal carcinoma and to enhance Dukes' classification. Dukes' and Jass' histopathological classifications were determined in 91 patients who had undergone curative resection for cancer of the colon (n = 51) or rectum (n = 40) and followed up for a minimum of 10 years. PCNA immunohistochemistry was possible in 79 tumours. Univariate analysis revealed that Jass' (P < 0.0001) and Dukes' classifications (P < 0.0002) were powerful predictors of survival but that the PCNA index had little prognostic power (P = 0.4). Multivariate analysis of both classifications showed similar predictive power and the PCNA index improved the prediction of survival when used with either classification for patients with colon cancer (chi 2 = 5.3, 1 d.f., P = 0.02 for each combination). The PCNA index, however, was not predictive for rectal cancer. Patients with the lowest PCNA index had the worst prognosis.

Expression of mutant p53 protein and CD44 variant proteins in colorectal tumorigenesis

Colorectal tumorigenesis evolves through a series of molecular genetic changes, providing putative markers for tumour progression. This study investigated the relation between expression of the tumour suppressor gene p53 and splice variants v5 and v6 of the cell adhesion molecule CD44 by immunohistochemistry on tissue samples of early adenomas (n = 12), late adneomas (n = 12), Dukes's A and B carcinomas (n = 21), and Dukes's C and D carcinomas (n = 22) and compared these results with expression of these proteins in normal colonic mucosa (n = 17). A statistically significant trend of increasing expression was seen for both p53 (p < 0.005) and CD44 variant exon v6 (p < 0.0005) in subsequent stages of this tumour progression model. High expression of CD44 v5 was seen in most colorectal neoplasms (83%-96%), independent of stage. A statistically significant correlation was present between p53 expression and expression of variant v6 of CD44 (p < 0.01). Both p53 expression and CD44 v6 expression in adenomas increased with the degree of dysplasia (p < 0.05). The results of this study show that mutant p53 protein and variant v6 of the CD44 glycoprotein are markers of tumour progression in colorectal cancer.

The common molecular genetic alterations in Dukes' B and C colorectal carcinomas are not short-term prognostic indicators of survival

Our study was undertaken to determine the prognostic significance of several common genetic alterations observed in colorectal carcinomas. We have previously analysed loss of heterozygosity of the MCC, APC, p53 and DCC tumour suppressor gene loci as well as p53 gene mutations and protein over-expression in a series of 100 Dukes' stage B and C colorectal tumours obtained at surgery. To extend our observations of alterations that may occur in these tumours, mutations to the c-Ki-ras oncogene and APC tumour suppressor gene were detected by PCR single-strand conformation polymorphism analysis. Short-term follow-up revealed no significant association between overall patient survival and any single, or combination of, genetic alteration(s). Surprisingly, patients whose tumours showed evidence of p53 protein over-expression/accumulation by immunocytochemistry (ICC) had a significantly better prognosis (p = 0.039) than those whose tumours had no p53 ICC reactivity.

Relationship of P-glycoprotein and carcinoembryonic antigen expression in human colon carcinoma to local invasion, DNA ploidy, and disease relapse

BACKGROUND

The clinical significance of expression of the MDR1 gene product P-glycoprotein (P-gp) in relation to the intrinsic drug resistance and progression of human colon cancer is largely unknown. To elucidate the role of P-gp in these cancers further, the frequency and intensity of P-gp and carcinoembryonic antigen (CEA) immunostaining were measured at the single-cell level and correlated with known prognostic indices (i.e., DNA ploidy, vessel/lymphatic microinvasion, histologic grade, and disease relapse).

METHODS

Fifty-two untreated Dukes' Stage B2 colon cancers were immunostained with the anti-P-gp monoclonal antibodies JSB-1 and HYB-241, and anti-CEA. DNA content and cell proliferation were measured by flow cytometry.

RESULTS

JSB-1 and HYB-241 detected P-gp in 44 and 42 of 52 carcinomas, respectively, and CEA was found in 50 of the 52 tumors. The level of P-gp expression was not associated with DNA ploidy, indices of local invasiveness, or histologic grade. In a multivariate analysis, however, a high level of P-gp expression (as assessed by JSB-1), DNA aneuploidy, microinvasion, and single carcinoma cell invasion individually predicted disease relapse (P < 0.05).

CONCLUSIONS

The results indicate that diffuse P-gp immunostaining is present in the majority of Stage B2 human colon cancers and therefore may be an important contributor to their intrinsic drug resistance. The association between a high level of P-gp expression and disease relapse suggests that P-gp can be of prognostic value in Stage B2 colon cancers.

Association of p53 expression with cytokinetics and HPV capsid antigen prevalence in oral carcinomas

p53 protein expression in oral squamous cell carcinomas (SCCs) was studied in relation to presence of HPV capsid antigens and tumour cell kinetics. The protein and viral antigens were determined from 64 SCCs employing immunoperoxidase and immunofluorescence techniques, respectively. Cell kinetics were assessed by in vitro bromodeoxyuridine labelling. Different levels of p53 were detected in 61% cases. Well-differentiated SCCs (88%) showed increased p53 expression compared with the less differentiated ones. In SCCs with higher cell proliferation rate (LI%, 13.25 +/- 4.64) the expression was almost absent. However, it was higher in stage I than in stage II/III carcinomas and occurred in 54.5% and 75% cases of HPV antigen-positive and -negative (or very little) SCCs, respectively.

p53 protein expression and prognosis in squamous cell carcinoma of the esophagus

BACKGROUND

The p53 gene product is known to regulate cell growth and proliferation. Whereas the wild-type p53 protein suppresses cell growth, the mutated p53 protein acts as an oncogene. Mutations in the p53 gene usually result in p53 protein stabilization and accumulation; so that the gene product can be detected by immunohistochemistry. Recently, the immunohistochemical detection of the p53 protein was associated with prognosis in breast, colorectal, and other types of cancer. However, its prognostic role in esophageal cancer remains to be elucidated.

METHODS

p53 expression in formalin fixed, paraffin embedded samples of 204 patients with primary squamous cell carcinoma of the esophagus, who underwent esophageal resection, were analyzed immunohistochemically with DO-1, a monoclonal antibody that detects wild-type and mutant forms of p53. The relationship between p53 immunoreactivity and prognostic factors was determined by the Chi-square test, and the prognostic impact of p53 protein expression was analyzed using univariate and multivariate survival analyses.

RESULTS

In 137 of 204 tumors (67.2%), nuclear immunoreactivity for the p53 protein was detected. There was no correlation with sex, age, pathologic tumor (pT) category, pathologic lymph node (pN) category, metastasis (M) category, residual cancer (R) category, histologic grade, or preoperative radiation therapy. In contrast to clinicopathologic parameters, p53 expression was not correlated with prognosis in univariate and multivariate survival analyses.

CONCLUSIONS

The p53 protein can be detected by immunohistochemistry in a high percentage of squamous cell carcinomas of the esophagus. However, the overexpression of the p53 gene product has no impact on the prognosis.

Comparison of p53 gene mutation and protein overexpression in colorectal carcinomas

Immunocytochemistry (ICC) has been used routinely to stain for p53 overexpression in a range of human tumours. The underlying assumption has been that positive staining indicates a mutation in the p53 coding sequence. Recently, however, discordancy has been observed and the accuracy of ICC as a marker of p53 gene mutation has been questioned. In this study of 109 colorectal adenocarcinomas, we compared ICC staining with p53 gene mutations detected by single-strand conformation polymorphism (SSCP) analysis. Concordancy between the two techniques was found in 69% of tumours. ICC-positive/SSCP-negative cases accounted for 20% of tumours and ICC-negative/SSCP-positive cases for the remaining 11%. These results caution against the assumption that p53 protein overexpression is always associated with a gene mutation. Epigenetic phenomena may account for a significant proportion of ICC-positive tumours.

Allelic loss of chromosome 18q and prognosis in colorectal cancer

BACKGROUND

Colorectal cancer occurs in approximately 150,000 people each year in the United States. Prognostic assessment influences the treatment of patients with colorectal cancer, including decisions about adjuvant therapy. We evaluated chromosome 18q allelic loss, a genetic event associated with tumor progression, as a prognostic marker for this disease.

METHODS

We developed procedures to examine the status of chromosome 18q with microsatellite markers and DNA from formalin-fixed, paraffin-embedded tumors. Allelic loss of chromosome 18q was assessed in 145 consecutively resected stage II or III colorectal carcinomas.

RESULTS

Among patients with stage II disease, the five-year survival rate was 93 percent in those whose tumor had no evidence of allelic loss of chromosome 18q and 54 percent in those with allelic loss; among patients with stage III disease, survival was 52 and 38 percent, respectively. The overall estimated hazard ratio for death in patients whose tumor had chromosome 18q allelic loss was 2.83 (P = 0.008) according to univariate analysis. Furthermore, chromosome 18q allelic loss remained a strong predictive factor (hazard ratio for death, 2.46; 95 percent confidence interval, 1.06 to 5.71; P = 0.036) after adjustment for all other evaluated factors, including tumor differentiation, vein invasion, and TNM stage.

CONCLUSIONS

The status of chromosome 18q has strong prognostic value in patients with stage II colorectal cancer. The prognosis in patients with stage II cancer and chromosome 18q allelic loss is similar to that in patients with stage III cancer, who are thought to benefit from adjuvant therapy. In contrast, patients with stage II disease who do not have chromosome 18q allelic loss in their tumor have a survival rate similar to that of patients with stage I disease and may not require additional therapy.

From Dukes through Jass: pathological prognostic indicators in rectal cancer

In the recently described Jass staging system for resected adenocarcinoma of the rectum, peritumoral lymphocytic infiltration and tumor growth pattern are introduced as significant indicators of prognosis in conjunction with depth of tumor invasion and lymph node metastasis. The authors of this study have tested the applicability of the Jass system by reviewing 348 resected rectal cancers for 12 pathological variables, including two newly recognized features, namely the Crohn's-like lymphoid reaction and metastatic tumor nodules in pericolic fat. By univariate analysis improved 5-year survival rate was associated with tubular-type adenocarcinoma, low tumor grade, retention of tubule configuration and nuclear polarity, expanding tumor growth pattern, prominent peritumoral lymphocytic infiltration, absence of extramural vein invasion by tumor, all levels of intramural and extramural invasion short of widespread local tumor dissemination, a Crohn's-like lymphoid reaction pattern, and absence of both nodal metastasis and tumor nodules in perirectal fat. By Cox stepwise proportional hazards analysis, depth of tumor invasion, lymph node metastasis, Crohn's-like lymphoid reaction, and extramural venous invasion retained independent prognostic significance. Peritumoral lymphocytic infiltration and tumor growth pattern of the Jass staging system failed to compete successfully with other variables in the proportional hazards model, in part because of their correlation with the model's selected variables. Both intramural and extramural extent of tumor invasion coupled with lymph node metastasis form the cornerstones of rectal cancer staging. However, other factors do refine prognostication. From this study the Crohn's-like lymphoid reaction emerges as a significant new independent indicator of prognosis for survival from rectal cancer. Although the Crohn's-like lymphoid reaction and extramural vein invasion took precedence as staging variables in this study, a complex interrelationship with other parameters was observed.

Association of p53 mutations with short survival in colorectal cancer

BACKGROUND/AIMS

Mutations in p53, a tumor suppressor gene located on chromosome 17p, are the most frequent genetic alterations found in human cancers. Increased intracellular concentration of p53, which is frequently but not systematically related to p53 mutation, has been proposed to be associated with poor prognosis in some tumor types. In colorectal cancer, this significance is still a matter of debate. To directly investigate the relationship between prognosis and p53 mutation, this study screened a series of 85 colorectal carcinomas for mutations in exons 5-8 of this gene.

METHODS

Polymerase chain reaction-amplified products from tumor DNA were analyzed by denaturing gradient gel electrophoresis and direct DNA sequencing.

RESULTS

Forty-four tumors were found to be mutated (52%). A strong correlation between the presence of a mutation and short survival was observed (P = 0.003). When tumors were classified according to their histological stage, a multivariate Cox model analysis showed that p53 mutation, rather than 17p allelic loss (previously proposed to convey prognostic information), was retained as the only independent prognostic factor (relative risk, 2.25; 95% confidence interval, 1.06-4.80; P < 0.029).

CONCLUSIONS

Combined with staging, direct monitoring of p53 mutation improves prognostic accuracy for colorectal cancer.

Neoplastic progression of human and rat intestinal cell lines after transfer of the ras and polyoma middle T oncogenes

BACKGROUND

Activation of the p21ras and pp60c-src oncoproteins occurred at high incidence in the early stage of human colorectal carcinogenesis. Our study aimed to investigate the role of these signal-transduction pathways in the process of initiation and promotion of the malignant phenotype in intestinal cells.

METHODS

The human Ha-ras and the polyoma middle T (Py-MT) viral oncogenes were transferred into large T oncogene of simian virus 40 immortalized rat intestinal epithelial SLC-44 cells and human colonic adenocarcinoma Caco-2 cells.

RESULTS

These transfers conferred the tumorigenic and invasive phenotypes on immortalized SLC-44 cells and potentiated the tumorigenicity of Caco-2 cells and markedly repressed the terminal differentiation of this cell line. In SLC-44T cells, induction of the invasive phenotype by the activated Ha-ras oncogene correlated with weak expression of E-cadherin and reduced accumulation of the transcripts encoding the basement membrane components alpha 1 (IV) collagen, nidogen, and BM40, which might result partly from the inactivation of the transforming growth factor beta signaling pathway. The down-regulation of the alpha 1 (IV) collagen messenger RNA in SLC-44T cells was not due to the protein kinase C-dependent pathways or the secretion of autocrine factor(s).

CONCLUSIONS

These results suggest that the activation of the p21ras and Py-MT/pp60c-src oncogenic pathways are critical effectors at different stages of colorectal carcinogenesis and in Caco-2 cells interferes with the program of enterocyte differentiation.

Prognostic significance of p53 expression in relation to DNA ploidy in colorectal adenocarcinoma

p53 expression, DNA ploidy and S-phase fraction were analysed retrospectively in colorectal adenocarcinomas from 293 patients in whom the long-term outcome was known. The frequency of nuclear p53 staining was increased in non-diploid tumours (42%) when compared with diploid tumours (33%). Cytoplasmic p53 positive tumours were more common in the proximal colon (32%) than in the distal sites (21%). In univariate survival analysis, nuclear p53 and cytoplasmic staining were significantly associated with poor prognosis in patients with Dukes' A-C tumours. The patients showing both nuclear and cytoplasmic p53 staining had the poorest survival and the patients with tumours negative in both the nucleus and cytoplasm showed the best prognosis. The patients with tumours positive in the nucleus alone or in the cytoplasm alone presented an intermediate survival. In multivariate survival analyses, nuclear p53 expression, cytoplasmic p53 expression and DNA ploidy were prognostic indicators independent of Dukes' stage and each other. Further analysis suggested that the prognostic importance of cytoplasmic p53 expression was greater in diploid than in non-diploid tumours. We conclude that nuclear p53 expression, cytoplasmic p53 expression and DNA ploidy provide important prognostic information in colorectal adenocarcinomas.

Tumourigenesis associated with the p53 tumour suppressor gene

The p53 gene is contained within 16-20 kb of cellular DNA located on the short arm of human chromosome 17 at position 17p13.1. This gene encodes a 393-amino-acid nuclear phosphoprotein involved in the regulation of cell proliferation. Current evidence suggests that loss of normal p53 function is associated with cell transformation in vitro and development of neoplasms in vivo. More than 50% of human malignancies of epithelial, mesenchymal, haematopoietic, lymphoid, and central nervous system origin analysed thus far, were shown to contain an altered p53 gene. The oncoproteins derived from several tumour viruses, including the SV40 large T antigen, the adenovirus E1B protein and papillomavirus E6 protein, as well as specific cellular gene products, e.g. murine double minute-2 (MDM2), were found to bind to the wild-type p53 protein and presumably lead to inactivation of this gene product. Therefore, the inactivation of p53 tumour suppressor gene is currently regarded as an almost universal step in the development of human cancers. The current data on p53-associated tumourigenesis are briefly discussed in this minireview.