SNaPshot and StripAssay as valuable alternatives to direct sequencing for KRAS mutation detection in colon cancer routine diagnostics.

Although direct sequencing is the gold standard for KRAS mutation detection in routine diagnostics, it remains laborious, time consuming, and not very sensitive. Our objective was to evaluate SNaPshot and the KRAS StripAssay as alternatives to sequencing for KRAS mutation detection in daily practice. KRAS exon 2-specific PCR followed by sequencing or by a SNaPshot reaction was performed. For the StripAssay, a mutant-enriched PCR was followed by hybridization to KRAS-specific probes bound to a nitrocellulose strip. To test sensitivities, dilution series of mutated DNA in wild-type DNA were made. Additionally, direct sequencing and SNaPshot were evaluated in 296 colon cancer samples. Detection limits of direct sequencing, SNaPshot, and StripAssay were 20%, 10%, and 1% tumor cells, respectively. Direct sequencing and SNaPshot can detect all 12 mutations in KRAS codons 12 and 13, whereas the StripAssay detects 10 of the most frequent ones. Workload and time to results are comparable for SNaPshot and direct sequencing. SNaPshot is flexible and easy to multiplex. The StripAssay is less time consuming for daily laboratory practice. SNaPshot is more flexible and slightly more sensitive than direct sequencing. The clinical evaluation showed comparable performances between direct sequencing and SNaPshot. The StripAssay is rapid and an extremely sensitive assay that could be considered when few tumor cells are available. However, found mutants should be confirmed to avoid risk of false positives.

Rapid genotyping of human papillomavirus by post-PCR array-based hybridization techniques.

Kinetic hybridization measurements on a microarray are expected to become a valuable tool for genotyping applications. A method has been developed that enables kinetic hybridization measurements of PCR products on a low-density microarray. This is accomplished by pumping a solution containing PCR products up and down through a porous microarray substrate. After every pumping cycle, the fluorescently labeled PCR products hybridized to capture probes immobilized on the solid surface of the porous microarray substrate are measured. By this method, both binding curves and high-resolution melting curves are obtained instead of the single endpoint hybridization intensities as with commonly used post-PCR array-based hybridization techniques. We used 20 subtypes of the human papillomavirus (HPV) as a model system to test our detection method and blindly analyzed 216 clinical samples. We compared our microarray flowthrough method with a reference method, PCR followed by a reverse line blot (RLB). Real-time hybridization measurements followed by high-resolution melting curves of low concentrations of fluorescently labeled HPV targets on a microarray were successfully carried out without any additional chemical signal amplification. The results of our new method were in good agreement (93%, with a kappa coefficient of κ = 0.88 [95% CI, 0.81 to 0.94]) with the RLB results. All discrepant samples were analyzed by a third method, enzyme immunoassay (EIA). Furthermore, in a number of cases, we were able to identify false-positive samples by making use of the information contained in the kinetic binding and melting curves. This clearly demonstrates the added value of the use of kinetic measurements and high-resolution melting curves, especially for highly homologous targets.

Thymidylate synthase genotyping is more predictive for therapy response than immunohistochemistry in patients with colon cancer.

Thymidylate synthase (TS) is a potentially valuable marker for therapy response since it is the molecular target of 5-fluorouracil (5-FU). TS can be analyzed at the DNA (gene polymorphisms and amplification) and protein level (immunohistochemistry). This study investigated the predictive role of TS at the DNA and protein levels in patients with N(+) colon cancer (n = 38). Tumor and normal tissues were genotyped using PCR for variable number of tandem repeats (VNTR), a single nucleotide polymorphism (SNP) in the 3R allele and a 6 bp deletion (1494del6) in the TS gene. Tumor tissues were additionally analyzed for loss of heterozygosity (VNTR polymorphism). A newly developed real time PCR assay was used to detect the presence of TS gene amplifications in tumor tissues. VNTR analysis in normal tissue was significantly associated with distant tumor recurrence (8% for 2R/2R vs. 52% for patients carrying a 3R allele, p = 0.038) and cancer-specific survival (p = 0.021). IHC was not found to be significantly associated with patients' outcome. No correlations between TS gene polymorphisms and IHC were found. However, TS gene amplification was correlated with a strong IHC staining intensity. In conclusion, this study indicates that DNA based analysis is more predictive for patients' outcome than TS IHC.

Detection of HER2 amplification in breast carcinomas: comparison of Multiplex Ligation-dependent Probe Amplification (MLPA) and Fluorescence In Situ Hybridization (FISH) combined with automated spot counting.

In this study the detection of HER2 gene amplification was evaluated using Fluorescence In Situ Hybridization (FISH; PathVysion) in comparison with Multiplex Ligation-dependent Probe Amplification (MLPA), a PCR based technique. These two methods were evaluated on a series of 46 formalin fixed paraffin embedded breast carcinomas, previously tested for protein overexpression by HercepTest (grouped into Hercep 1+, 2+ and 3+). HER2 gene amplification (ratio > or =2.0) by FISH was found in 9/10, 10/30 and 0/6 in IHC 3+, 2+ and 1+/0 cases, respectively. Digitalized automated spot counting performed with recently developed CW4000 CytoFISH software was 100% concordant with manual FISH scoring. Using MLPA 18/46 samples showed a clear HER2 amplification. Comparing MLPA and IHC showed the same results as for FISH and IHC. All but one FISH positive cases (18/19) were confirmed by MLPA for the presence of the gene amplification. The overall concordance of detection of Her2 gene amplification by FISH and MLPA was 98% (45/46). Furthermore, both the level of amplification and equivocal results correlated well between both methods. In conclusion, MLPA is a reliable and reproducible technique and can be used as an either alternative or additional test to determine HER2 status in breast carcinomas.

Tumor-associated zinc finger mutations in the CTCF transcription factor selectively alter tts DNA-binding specificity.

CTCF is a widely expressed 11-zinc finger (ZF) transcription factor that is involved in different aspects of gene regulation including promoter activation or repression, hormone-responsive gene silencing, methylation-dependent chromatin insulation, and genomic imprinting. Because CTCF targets include oncogenes and tumor suppressor genes, we screened over 100 human tumor samples for mutations that might disrupt CTCF activity. We did not observe any CTCF mutations leading to truncations/premature stops. Rather, in breast, prostate, and Wilms' tumors, we observed four different CTCF somatic missense mutations involving amino acids within the ZF domain. Each ZF mutation abrogated CTCF binding to a subset of target sites within the promoters/insulators of certain genes involved in regulating cell proliferation but did not alter binding to the regulatory sequences of other genes. These observations suggest that CTCF may represent a novel tumor suppressor gene that displays tumor-specific "change of function" rather than complete "loss of function."