Clinical significance of K-Ras mutations in intraoperative tumor drainage blood from patients with colorectal carcinoma

Is K-ras gene mutation a prognostic factor for colorectal cancer: a systematic review and meta-analysis

BACKGROUND

: The K-ras gene is one of the commonly mutated oncogenes associated with colorectal cancer. However, its prognostic significance for patients with colorectal cancer remains inconclusive.

OBJECTIVE

: To derive a more precise estimation of the prognostic significance of K-ras gene mutations, a systematic review and meta-analysis were performed.

DATA SOURCES

: We searched PubMed, Embase, and the Cochrane databases from January 1992 to November 2011.

STUDY SELECTION

: The prognostic value of K-ras gene mutations was examined in patients with colorectal cancer who did not receive preoperative chemotherapy or radiation.

MAIN OUTCOME MEASURES

: The effect of K-ras gene mutations on the overall survival was measured by the HR and 95% CIs.

RESULTS

: The pooled HR for the association between K-ras gene mutations and overall survival in patients with colorectal cancer was 1.04 (95% CI: 0.99-1.10, p = 0.11). Subgroup analysis showed significant reductions in the overall survival associated with mutations at K-ras codon 12, the articles that reported HR directly, and the studies published before and after 2005, although publication bias was present. All the associations disappeared after adjustment with the trim-and-fill method. The pooled HR of 3 studies examining mutations at K-ras codon 13 was 1.47 (95% CI: 1.09-1.97, p = 0.02), and no publication bias was observed. No significant association was observed in different study regions.

LIMITATIONS

: The heterogeneity in the study populations is a potential problem, the use of different staging systems or small groups of different stages may contribute to heterogeneity, and residual confounding may have influenced the results in those studies that did not completely adjust for other factors.

CONCLUSIONS

: Overall K-ras gene mutations seem not to correlate with the prognosis of patients with colorectal cancer. The association remains to be confirmed with a more precise analysis of a large sample.

Sensitive quantitative assay for point mutations in the rat H-ras gene based on single nucleotide primer extension

Point mutations in oncogenes and tumor suppressor genes occur at early stages in the carcinogenic process. Point mutations in ras family oncogenes are the most common mutational events in several types of human cancer, and are available as molecular markers for the detection of cancer cells in carcinogenicity bioassay systems as well as in clinical samples. Although several techniques are utilized to detect point mutations in carcinogenicity bioassay systems, the sensitivity is too low to determine a small number of mutations. In order to overcome the disadvantage and to sensitively determine gene mutation rates for in vivo carcinogenicity bioassays of presumptive carcinogens, we established a Thermosequenase Cycle End Labeling (TCEL) method, a sensitive approach based on single nucleotide primer extension. One of the characteristics of the method is a high sensitivity of 1:100,000, ten times the sensitivity of the mutant allele-specific amplification now commonly employed. Using TCEL, we here quantified H-ras mutations in the livers of rats treated with a genotoxic carcinogen, 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline. Our findings suggest that this method may be applied for many genetic targets as a component in vivo.

Meta-analysis shows that detection of circulating tumor cells indicates poor prognosis in patients with colorectal cancer

BACKGROUND & AIMS

The prognostic significance of circulating (CTCs) and disseminated tumor cells in patients with colorectal cancer (CRC) is controversial. We performed a meta-analysis of available studies to assess whether the detection of tumor cells in the blood and bone marrow (BM) of patients diagnosed with primary CRC can be used as a prognostic factor.

METHODS

We searched the Medline, Biosis, Science Citation Index, and Embase databases and reference lists of relevant articles (including review articles) for studies that assessed the prognostic relevance of tumor cell detection in the peripheral blood (PB), mesenteric/portal blood (MPB), or BM of patients with CRC. Meta-analyses were performed using a random effects model, with hazard ratio (HR) and 95% confidence intervals (95% CIs) as effect measures.

RESULTS

A total of 36 studies, including 3094 patients, were eligible for final analyses. Pooled analyses that combined all sampling sites (PB, MPB, and BM) associated the detection of tumor cells with poor recurrence-free survival (RFS) (HR = 3.24 [95% CI: 2.06-5.10], n = 26, I(2) = 77%) and overall survival (OS) (2.28 [1.55-3.38], n = 21, I(2) = 66%). Stratification by sampling site showed that detection of tumor cells in the PB compartment was a statistically significant prognostic factor (RFS: 3.06 [1.74-5.38], n = 19, I(2) = 78%; OS: 2.70 [1.74-4.20], n = 16, I(2) = 59%) but not in the MPB (RFS: 4.12 [1.01-16.83], n = 8, I(2) = 75%; OS: 4.80 [0.81-28.32], n = 5, I(2) = 82%) or in the BM (RFS: 2.17 [0.94-5.03], n = 4, I(2) = 78%; OS: 1.50 [0.52-4.32], n = 3, I(2) = 84%).

CONCLUSION

Detection of CTCs in the PB indicates poor prognosis in patients with primary CRC.

DETECTION OF DISSEMINATED TUMOR CELLS IN PERIPHERAL BLOOD

Metastases are the major cause of cancer-related deaths in patients with solid epithelial malignancies, such as breast, colorectal and prostate carcinomas. Hematogenous spreading of tumor cells from a primary tumor can be considered as a crucial step in the metastasis cascade leading eventually to the formation of clinically manifest metastases. Consequently, as shown in recent studies, the detection of disseminated tumor cells in peripheral blood might be of clinical relevance with respect to individual patient prognosis and staging or monitoring of therapy. However, the rarity of disseminated tumor cells in peripheral blood renders the application of sensitive techniques mandatory for their detection. The emergence of highly sophisticated reverse transciptase-polymerase chain reaction (RT-PCR) assays, combining a preanalytical enrichment step with the assessment of multiple molecular tumor markers expressed in disseminated tumor cells, provides a powerful tool in detecting disseminated tumor cells with high sensitivity and specificity. This review will discuss currently used tumor markers as well as experimental means to enhance the sensitivity and specificity of RT-PCR assays to detect disseminated tumor cells in the peripheral blood of patients with breast, colorectal, and prostate cancers, and their clinical relevance assessed in recent studies.

Clinical significance of TROP2 expression in colorectal cancer

PURPOSE AND EXPERIMENTAL DESIGN

To identify cancer-related genes, the expression profiles of colorectal cancer cells and normal epithelial cells were examined and compared using laser microdissection and cDNA microarray analysis. From these combined techniques, several cancer-related genes, including TROP2, were identified. TROP2 is known as a calcium signal transducer and is highly expressed in several types of tumors. However, no studies have investigated the significance of TROP2 expression in colorectal cancer. Thus, the expression status of TROP2 was investigated in 74 colorectal cancer samples by quantitative real-time reverse transcription-PCR and immunohistochemical studies.

RESULTS

Laser microdissection and cDNA microarray analysis showed that there were 84 overexpressed genes in cancer cells. One of the highly overexpressed genes was TROP2. Quantitative real-time reverse transcription-PCR showed that TROP2 expression in cancer samples was significantly higher than in normal samples (P < 0.001). The samples were divided into high (n = 26) and low (n = 48) TROP2 expression groups. The cases with high TROP2 expression showed a higher frequency of liver metastasis (P = 0.005) and more cancer-related death (P = 0.046). Those cases also had an inclination of deeper depth of invasion (P = 0.064) and more lymph node metastasis (P = 0.125). Interestingly, the patients with high TROP2 expression tumors had poorer prognosis (P = 0.0036). Multivariate analysis showed that TROP2 expression status was an independent prognostic factor (relative risk, 2.38; 95% confidence interval, 1.29-4.74; P < 0.01).

CONCLUSION

TROP2 is one of the cancer-related genes that correlates with biological aggressiveness and poor prognosis of colorectal cancer. Thus, TROP2 is a possible candidate gene for diagnosis and molecular target therapy of colorectal cancer.

Detection of isolated tumor cells by polymerase chain reaction-restriction fragment length polymorphism for K-ras mutations in tissue samples of 199 colorectal cancer patients

The aim of this study was to identify K-ras mutations as marker for isolated tumor cells in liver, lymph node, and bone marrow specimens of colorectal cancer patients. To detect these, a PCR-RFLP assay was used with a sensitivity exceeding that of routine histopathology by at least 1 order of magnitude. In addition, the ratio of mutated versus wild-type alleles was determined by an internal standard. Of 199 patients, 74 (37.5%) were found to bear a K-ras-positive tumor. Of these, 60 (81%) were mutated in codon 12 and 14 (19%) in codon 13 (P < 0.001). In addition, 14 organs were found K-ras positive, 13 of which were from 12 patients with a K-ras-positive tumor (16%) and 1 from a patient with a K-ras-negative tumor (0.8%). Eight patients exhibited liver involvement and 6 showed lymph node involvement. Remarkably, no bone marrow specimen was found K-ras positive (P < 0.017 versus liver involvement). Sequence analysis of tumor DNA revealed that GGT (Gly) was replaced by GAT (Asp; 35%), GTT (Val; 32%), AGT (Ser; 13%), GCT (Ala; 10%), TGT (Cys; 8%), and CGT (Arg; 2%) for codon 12, and by GAC (Asp) as the only type of mutation for codon 13. In colorectal carcinomas the ratio of K-ras mutated versus wild-type alleles ranged over 4 orders of magnitude (10(0)-10(-4), median: 10(-2)) and was correlated with both, residual tumor load (R1/2; P = 0.028) and distant metastasis (M1; P = 0.057). These results show that detection of K-ras mutated alleles by PCR-RFLP in patients with colorectal carcinoma may aid in the identification of isolated tumor cells. High ratios of K-ras alleles were correlated with certain negative prognostic parameters (R,M). In accord with its function as a primary filter for colorectal carcinoma cells, the liver was more often contaminated with K-ras-positive cells than bone marrow.

Molecular assessment of depth of myometrial invasion in stage I endometrial cancer: a model based on K-ras mutation analysis

INTRODUCTION

Overall nearly 20% of endometrial cancer (EC) patients die of the disease and over half of these had initially presented with clinical stage I disease. There is a strong correlation between disease mortality and depth of myometrial invasion. Current assessment of depth of invasion relies on light microscopy. Tumor cells can evade detection by light microscopy if they are vastly outnumbered by myometrial cells. Molecular techniques have a great potential in the detection of such isolated cells.

OBJECTIVE

The objective was to develop a model for the application of molecular techniques to advance the assessment of risk status in patients with clinical stage I EC.

METHODS

The study sample included 21 stage I ECs with a documented K-ras mutation from two series of 96 and 106 ECs from the United Kingdom and Norway, respectively. K-ras was documented using heteroduplex mobility analysis and amplified created restriction site, followed by sequencing to identify the specific base substitution at codon 12 and 13 of K-ras oncogene. For each case with a K-ras mutation, a modified mutant allele-specific amplification technique was carried out on a series of tissue strips microdissected at increasing depths from the myometrium underlying tumor. The microdissected myometrium had been previously examined histologically for absence of infiltrating tumor cells on light microscopy. Presence of K-ras mutations was used to identify the tumor cells within the histologically normal myometrium. Correlations between submicroscopic myometrial tumor cell infiltration and clinicopathological factors were studied.

RESULTS

Of 21 cases with K-ras mutation, 6 cases (28%) showed molecular evidence of tumor cell infiltration beyond the histological boundary. The depth of submicroscopic myometrial infiltration was found to be variable. The staging of the tumors would have changed in 3 cases (14%) if tumor cells been detected histologically. A borderline significant correlation between presence of submicroscopic myometrial invasion and depth of myometrial invasion was noted (P = 0.053). The recurrence rate and survival of patients without submicroscopic invasion were better than those with, although it did not reach statistical significance (recurrence rate P = 0.13, recurrence free survival P = 0.14, cause-specific survival P = 0.12, and total survival P = 0.2).

CONCLUSIONS

Molecular assessment of depth of myometrial invasion using K-ras mutation is feasible and may add information to conventional light microscopy. Further prospective studies are required to define the clinical significance of this technology.

Micrometastasis in colorectal cancer

Colorectal cancer is one of the most common malignancies in the word and can be usually cured if diagnosed at an early stage. In the European area the estimated number of new cases of cancer in 1995 were approximately 334.000 and 189.000 died of cancer in that year. Despite recent progress in early detection and surgical therapy, the mortality remained unchanged over the past decades. The major reason for this disturbing discrepancy is that occult dissemination of viable cancer cells can occur at any stage of tumorigenesis. Occult dissemination of the tumor cells in patients with operable cancer may be considered a determinant of subsequent metastasis formation. Several groups have therefore designed immunocytochemical and molecular assays to identify such minimal amounts of residual tumor cells that have successfully invaded secondary organs. The question whether circulating tumor cells represent metastatic dissemination or are merely cancer cells without metastatic potential that have detached from the primary tumor, has been debated for over half a century.

Development of a simple and sensitive technique for detection of point mutations in the K-ras oncogene

We sought to develop a simple and sensitive method based on mutant allele-specific amplification (MASA) for the detection of point mutations in the k-ras oncogene in blood samples. We used MASA and three nested MASA methods to detect a point mutation (GGT-->GAT) in rat DHD cells at codon 12 of exon 1 of the k-ras gene. MASA allowed us to detect one k-ras mutated cell on a background of 10(7) normal cells. The third nested-MASA (nested-MASA.c) method that we developed allowed us to detect one mutated cell among 10(10) normal cells. Our methods should allow the detection of small amounts of mutant k-ras DNA in tissue, serum, and plasma, combining speed with efficiency and specificity.