Molecular Testing in Colorectal Carcinoma

e15069 Background: Recent clinical guidelines for expansion of molecular testing of oncogenic RAS mutations in colorectal carcinoma have led to increased identification of mutations in this patient population. The clinical characteristics of NRAS-mutated colorectal carcinoma have not been well established because of the lower prevalence of these mutations (< 6%) as compared to oncogenic KRAS mutations. Here, we report the discovery of a novel internal tandem duplication (ITD) mutation of NRAS, which disrupts the Switch II domain in an index case of a patient with widely disseminated colorectal cancer. Methods: Hotspot next generation sequencing of a brain metastasis using a clinical solid tumor panel identified this novel NRAS ITD and a TP53 missense mutation (p.P275F). Whole exome sequencing of the primary tumor and two metastatic lesions (lung and brain) was performed to identify other genetic factors potentially driving the disease. Results: The above approach confirmed that the NRAS ITD and TP53 mutation were conserved between the primary tumor and both metastatic tumors and identified an additional pathogenic mutation in CSMD1 (a tumor suppressor gene). No other clearly pathogenic driver mutations were identified. Structural biology and biochemical analyses demonstrated that the inserted 15 amino acids prevented binding to GAP protein, leading to sustained RAS activation and increased interaction with RAF to stimulate downstream MAPK activation. Conclusions: These genomic and biochemical studies indicate that a novel NRAS ITD was the primary driver mutation of this aggressive colorectal carcinoma. Identical or similar ITDs in NRAS and KRAS may also drive other forms of colorectal cancer and other aggressive malignancies and represent a new subset of RAS-driven drug-resistant cancers.

Download Full-text

Validating a fully automated real-time PCR-based system for use in the molecular diagnostic analysis of colorectal carcinoma: a comparison with NGS and IHC

Journal of Clinical Pathology ◽

10.1136/jclinpath-2017-204356 ◽

2017 ◽

Vol 70 (7) ◽

pp. 610-614 ◽

Cited By ~ 19

Author(s):

Richard Colling ◽

Lai Mun Wang ◽

Elizabeth Soilleux

Keyword(s):

Colorectal Carcinoma ◽

Digital Pcr ◽

Molecular Diagnostic ◽

Molecular Testing ◽

Formalin Fixed Paraffin ◽

Formalin Fixed Paraffin Embedded ◽

Polymerase Chain ◽

Next Generation Sequencing Ngs ◽

Generation Sequencing ◽

Formalin Fixed

BackgroundMolecular testing is increasingly needed in colorectal carcinoma (CRC) and the current clinically relevant mutations are in BRAF, KRAS and NRAS. This study aimed to further validate a new alternative polymerase chain reaction (PCR) platform (Idylla, Biocartis) against existing next-generation sequencing (NGS) and immunohistochemistry (IHC) assays.Methods56 Idylla tests were performed on 43 CRC cases, in a total of 74 comparisons against an NGS panel (Ion Torrent) and the VE1 (anti-BRAF) antibody IHC. Discrepant cases were also compared with either conventional (Cobas) or droplet digital PCR (Bio-Rad).ResultsIdylla showed an overall concordance of 100% (95% CI 93% to 100%) with comparator molecular testing and indications were that Idylla is likely to be more sensitive than routine NGS. BRAF IHC showed 90% concordance with NGS (95% CI 70% to 97%).ConclusionsThis study validates Idylla in formalin-fixed, paraffin-embedded CRC tissue. BRAF IHC, however, is an unreliable substitute for molecular testing in CRC.

Download Full-text