Another concern that testing of small biopsies would be inaccurate also proved unfounded, with an assay failure rate of only 4%, and the concordance between KRAS mutation assays of matched samples from the multiple biopsies and resected tumour was 99%,36 showing the reliability of DNA-based assays of colon cancer biopsies. The gene discussed is KRAS; the disease is malignant colon neoplasm.