Risk for molecular contamination of tissue samples evaluated for targeted anti-cancer therapy

How to Set Up a Molecular Pathology Lab: A Guide for Pathologists

In today's pathology practice, pathologists combine molecular tests with conventional histopathological methods. Pathology laboratories should therefore be designed and operated in accordance with the requirements of molecular testing procedures. While the specifics of the requirements may vary depending on the spectrum of the tests that will be performed, there are several basic criteria that need to be fulfilled for standardization. Adequate space, appropriate equipment and qualified personnel are required to establish a molecular pathology laboratory. One of the most important points that should be taken into consideration while designing a molecular pathology laboratory is to create a plan to prevent contamination. As molecular diagnosis has a major role in treatment decisions, the management of the molecular pathology laboratory is of utmost importance. In this review, the criteria required to establish an optimal molecular pathology laboratory will be reviewed.

STR technique for the detection of contamination by exogenous DNA in paraffin blocks and histological slides

Gastrointestinal Stromal Tumors (GIST) present different types of mutations that may or may not be sensitive to specific target therapy. The laboratory procedure required to prepare histological sections traditionally demands multiple steps, making the process prone to contamination by exogenous genetic material (DNA). An eventual contamination of the biological sample with exogenous DNA may jeopardize subsequent analysis of mutations. The Short Tandem Repeat (STR) technique is frequently used in forensic science fields and presents a potential application in surgical pathology, especially in situations of suspected sample exchange. In the present study, the objective is to verify the possible contamination by exogenous DNA in gastric GIST samples and to evaluate if the presence of contamination can interfere in the detection of the mutations of interest. We assessed eight gastric GISTs by the Sanger sequencing and STR sequence analyses. Seven samples presented more than one profile, a result interpreted as contamination. Our results indicate that exogenous DNA contamination occurred in most of the samples studied and that this was more frequent in samples obtained from the slides than those obtained from the block. The presence of contamination did not inhibit the detection of the mutations of interest for a specific target therapy. Furthermore, the histologic block revealed to be more advantageously when compared to the slide for molecular pathology diagnosis.

Flex-Array® - a novel multi-well vessel system for the immobilization and multi-modal testing of intact formalin-fixed paraffin-embedded (FFPE) cells or tissues

Flex-Array® is a novel multi-well system that extends the key features of current high-performance microscope slides used in advanced staining techniques. The Flex-Array® system facilitates the immobilization of FFPE cell or tissue sections onto a multi-well array for the subsequent performance of single analyte (IHC) or multiplexed immunohistochemistry (MIHC). Additionally, the Flex-Array® device is compatible with fluorescent and colorimetric in situ hybridization (FISH) and adds new capabilities such as replicate analysis, quantitative ELISA-like assays and microdissection-free nucleic acid extraction. The Flex-Array® facilitates rapid, contextually rich and high-precision multi-modal analysis of FFPE cells and tissues at a significant reduction in testing, data acquisition and analysis costs.

ICESsuHN105, a Novel Multiple Antibiotic Resistant ICE in Streptococcus suis Serotype 5 Strain HN105

Streptococcussuis serotype 5, an emerging zoonosis bacterial pathogen, has been isolated from infections in both pigs and humans. In this study, we sequenced the first complete genome of a virulent, multidrug-resistant SS5 strain HN105. The strain HN105 displayed enhanced pathogenicity in zebrafish and BABL/c mouse infection models. Comparative genome analysis identified a novel 80K integrative conjugative element (ICE), ICESsuHN105, as required for the multidrug resistance phenotype. Six corresponding antibiotic resistance genes in this ICE were identified, namely tet (O), tet (M), erm (two copies), aph, and spc. Phylogenetic analysis classified the element as a homolog of the ICESa2603 family, containing the typical family backbone and insertion DNA. DNA hybrids mediated by natural transformation between HN105 and ZY05719 verified the antibiotic resistant genes of ICESsuHN105 that could be transferred successfully, while they were dispersedly inserted with a single gene in different genomic locations of ZY05719_(HN105) transformants. To further identify the horizontal transfer of ICESsuHN105 as a whole mobile genetic element, a circular intermediate form of ICESsuHN105 was detected by PCR. However, the effective conjugation using serotype 2 S. suis as recipients was not observed in current assays in vitro. Further studies confirmed the presence of the complete lantibiotic locus encoded in ICESsuHN105 that effectively inhibits the growth of other streptococci. In summary, this study demonstrated the presence of antibiotic resistance genes in ICE that are able to transfer between different clinical isolates and adapt to a broader range of Streptococcus serotype or species.

Multicenter Evaluation of the Idylla NRAS-BRAF Mutation Test in Metastatic Colorectal Cancer

Treatment of colorectal cancer (CRC) with monoclonal antibodies against epidermal growth factor receptor requires the assessment of the mutational status of exons 2, 3, and 4 of the NRAS and KRAS oncogenes. Moreover, the mutational status of exon 15 of the BRAF oncogene is a marker of poor prognosis in CRC. The Idylla NRAS-BRAF Mutation Test is a reliable, simple (<2 minutes hands-on time), and quick (<2 hours turnaround time) sample-to-result solution, enabling the detection of clinically relevant mutations in NRAS (18 mutations) and BRAF (5 mutations). A multicenter study was conducted in 14 centers using the Idylla NRAS-BRAF Mutation Test to assess the NRAS and BRAF mutational status of 418 formalin-fixed, paraffin-embedded tissue samples from CRC patients. Results were compared with those obtained earlier by routine reference methods, including next-generation sequencing, pyrosequencing, mass spectrometry-based assays, PCR-based assays, and Sanger sequencing. In case of discordance, additional tests were performed by digital droplet PCR. Overall, after testing confirmation and excluding invalids/errors by design, concordances between the Idylla NRAS-BRAF Mutation Test and the reference test results were found in almost perfect agreement. In conclusion, the Idylla NRAS-BRAF Mutation Test enables the routine detection of all NRAS and BRAF mutations deemed clinically relevant according to the latest clinical guidelines, without necessitating molecular expertise or infrastructure.

Mutant KRAS Circulating Tumor DNA Is an Accurate Tool for Pancreatic Cancer Monitoring

BACKGROUND

Many new pancreatic cancer treatment combinations have been discovered in recent years, yet the prognosis of pancreatic ductal adenocarcinoma (PDAC) remains grim. The advent of new treatments highlights the need for better monitoring tools for treatment response, to allow a timely switch between different therapeutic regimens. Circulating tumor DNA (ctDNA) is a tool for cancer detection and characterization with growing clinical use. However, currently, ctDNA is not used for monitoring treatment response. The high prevalence of KRAS hotspot mutations in PDAC suggests that mutant KRAS can be an efficient ctDNA marker for PDAC monitoring.

SUBJECTS, MATERIALS, AND METHODS

Seventeen metastatic PDAC patients were recruited and serial plasma samples were collected. CtDNA was extracted from the plasma, and KRAS mutation analysis was performed using next-generation sequencing and correlated with serum CA19-9 levels, imaging, and survival.

RESULTS

Plasma KRAS mutations were detected in 5/17 (29.4%) patients. KRAS ctDNA detection was associated with shorter survival (8 vs. 37.5 months). Our results show that, in ctDNA positive patients, ctDNA is at least comparable to CA19-9 as a marker for monitoring treatment response. Furthermore, the rate of ctDNA change was inversely correlated with survival.

CONCLUSION

Our results confirm that mutant KRAS ctDNA detection in metastatic PDAC patients is a poor prognostic marker. Additionally, we were able to show that mutant KRAS ctDNA analysis can be used to monitor treatment response in PDAC patients and that ctDNA dynamics is associated with survival. We suggest that ctDNA analysis in metastatic PDAC patients is a readily available tool for disease monitoring.

IMPLICATIONS FOR PRACTICE

Avoiding futile chemotherapy in metastatic pancreatic ductal adenocarcinoma (PDAC) patients by monitoring response to treatment is of utmost importance. A novel biomarker for monitoring treatment response in PDAC, using mutant KRAS circulating tumor DNA (ctDNA), is proposed. Results, although limited by small sample numbers, suggest that ctDNA can be an effective marker for disease monitoring and that ctDNA level over time is a better predictor of survival than the dynamics of the commonly used biomarker CA19-9. Therefore, ctDNA analysis can be a useful tool for monitoring PDAC treatment response. These results should be further validated in larger sample numbers.

Characterization of Factors Affecting the Detection Limit of EGFR p.T790M in Circulating Tumor DNA

OBJECTIVE

Circulating tumor DNA is a promising noninvasive tool for cancer monitoring. One of the challenges in applying this tool is the detection of low-frequency mutations. The detection limit of these mutations varies between different molecular methods. The aim of this study is to characterize the factors affecting the limit of detection for epidermal growth factor receptor p.T790M mutation in circulating tumor DNA of patients with lung adenocarcinoma.

METHODS

DNA was extracted from plasma samples of 102 patients. For sequencing the DNA, we used 2 different next-generation sequencing-based platforms: Ion Torrent Personal Genome Machine (56 cases) and Roche/454 (46 cases). Serially diluted synthetic DNA samples carrying the p.T790M mutation were sequenced using the Ion Torrent Personal Genome Machine for validation. Limit of detection was determined through the analysis of non-hot-spot nonreference reads, which were regarded as sequencing artifacts.

RESULTS

The frequency of the non-hot-spot nonreference reads was higher in Ion Torrent Personal Genome Machine compared to Roche/454 (0.07% ± 0.08% and 0.03% ± 0.06%, respectively, P < .001). We found that different base type substitutions occur with different frequency. Since the base substitution leading to p.T790M mutation is C>T transition, its frequency was used to determine the limit of detection for the assay. Based on the C>T non-hot-spot nonreference allele frequency, we found that the limit of detection is 0.18% in Ion Torrent Personal Genome Machine and 0.1% in Roche/454. Based on these values, 48% and 56% of the cases were positive for T790M mutation in Ion Torrent Personal Genome Machine and Roche/454 groups, respectively. Agreement between duplicates was 76% in Ion Torrent Personal Genome Machine and 72% in Roche/454. Using serially diluted synthetic DNA samples carrying the p.T790M mutation, we could identify mutations with allele frequency of 0.18% or more using the Ion Torrent Personal Genome Machine, supporting our approach to determine the detection limit.

CONCLUSION

Both the sequencing platform and the specific nucleotide change affect the limit of detection and should therefore be determined in the validation process of new assays.

Lung cancer mutation testing: a clinical retesting study of agreement between a real-time PCR and a mass spectrometry test

To investigate the clinical validity and utility of tests for detecting Epidermal Growth Factor Receptor (EGFR) gene mutations in non-squamous non-small cell lung cancer patients, tumour DNA extracts from 532 patients previously tested by the cobas EGFR Mutation Test (RT-PCR test) were retested by the Sequenom/Agena Biosciences MassArray OncoFocus mass spectrometry test (MS test). Valid results from both tests were available from 470 patients (88%) for agreement analysis. Survival data were obtained for 513 patients (96%) and 77 patients (14%) were treated with EGFR tyrosine kinase inhibitors (TKIs). Agreement analysis revealed moderately high positive (79.8%), negative (96.9%) and overall percentage agreement (93.2%) for the detection of EGFR mutations. However, EGFR mutations were detected by one test and not by the other test in 32 patients (7%). Retesting of discordant samples revealed false-positive and false-negative results generated by both tests. Despite this, treatment and survival outcomes correlated with the results of the RT-PCR and MS tests. In conclusion, this study provides evidence of the clinical validity and utility of the RT-PCR and MS tests for detection of EGFR mutations that predict prognosis and benefit from EGFR-TKI treatment. However, their false-positive and false-negative test results may have important clinical consequences.