title: Mutational analysis of primary and metastatic colorectal cancer samples underlying the resistance to cetuximab-based therapy.
abstract: OBJECTIVE
  Although several molecular markers predicting resistance to cetuximab- or panitumumab-based therapy of metastatic colorectal cancer were described, mutations in RAS proto-oncogenes remain the only predictors being used in daily clinical practice. However, 35%-45% of wild-type RAS patients still do not respond to this anti-epidermal growth factor receptor (anti-EGFR) monoclonal antibody-based therapy, and therefore the definition of other predictors forms an important clinical need. The aim of the present retrospective single-institutional study was to evaluate potential genes responsible for resistance to anti-EGFR therapy in relation to mutational analysis of primary versus metastatic lesions.
  
  
  METHODS
  Twenty-four paired primary and corresponding metastatic tissue samples from eight nonresponding and four responding metastatic colorectal cancer patients treated with cetuximab-based therapy were sequenced using a next-generation sequencing panel of 26 genes involved in EGFR signaling pathway and colorectal carcinogenesis.
  
  
  RESULTS
  Mutational status of primary tumors and metastatic lesions was highly concordant in TP53, APC, CTNNB1, KRAS, PIK3CA, PTEN, and FBXW7 genes. Metastatic samples harbor significantly more mutations than primary tumors. Potentially negative predictive value of FBXW7 mutations in relationship to anti-EGFR treatment outcomes was confirmed. Finally, new occurrences of activating KRAS mutations were identified in a group of patients initially determined as wild-type RAS by routinely used qPCR-based RAS mutational tests. All newly detected activating KRAS mutations most likely led to cetuximab treatment failure.
  
  
  CONCLUSIONS
  The results of the present study suggest a need of careful consideration of previously published results of anti-EGFR-targeted therapy with regard to potentially inaccurate diagnostic tools used in the past. Based on our findings, we recommend more extensive use of next-generation sequencing testing in daily clinical practice, as it brings a significant added value in terms of validity of the diagnostic procedure.
authors.affiliation: Department of Comprehensive Cancer Care, Masaryk Memorial Cancer Institute, Masaryk University, Brno, Czech Republic.
authors.forename: Radim
authors.initials: R
authors.lastname: Nemecek
authors.affiliation: Department of Oncological and Experimental Pathology, Masaryk Memorial Cancer Institute, Brno, Czech Republic.
authors.forename: Jitka
authors.initials: J
authors.lastname: Berkovcova
authors.affiliation: Central European Institute of Technology, Masaryk University, Brno, Czech Republic.
authors.forename: Lenka
authors.initials: L
authors.lastname: Radova
authors.affiliation: Department of Radiation Oncology, Masaryk Memorial Cancer Institute, Masaryk University, Brno, Czech Republic.
authors.forename: Tomas
authors.initials: T
authors.lastname: Kazda
authors.affiliation: Central European Institute of Technology, Masaryk University, Brno, Czech Republic.
authors.forename: Jitka
authors.initials: J
authors.lastname: Mlcochova
authors.affiliation: Department of Comprehensive Cancer Care, Masaryk Memorial Cancer Institute, Masaryk University, Brno, Czech Republic; Central European Institute of Technology, Masaryk University, Brno, Czech Republic.
authors.forename: Petra
authors.initials: P
authors.lastname: Vychytilova-Faltejskova
authors.affiliation: Department of Comprehensive Cancer Care, Masaryk Memorial Cancer Institute, Masaryk University, Brno, Czech Republic; Central European Institute of Technology, Masaryk University, Brno, Czech Republic.
authors.forename: Ondrej
authors.initials: O
authors.lastname: Slaby
authors.affiliation: Department of Comprehensive Cancer Care, Masaryk Memorial Cancer Institute, Masaryk University, Brno, Czech Republic.
authors.forename: Marek
authors.initials: M
authors.lastname: Svoboda
keywords: FBXW7; KRAS; cetuximab; colorectal cancer; next-generation sequencing; resistance to anti-EGFR therapy