Abstract
The major aim of this study was to evaluate the performance of anti-BRAF V600E (VE1) antibody in colorectal tumors with and without KRAS mutation. KRAS and BRAF are two major oncogenic drivers of colorectal cancer (CRC) that have been frequently described as mutually exclusive, thus the BRAF V600E mutation is not expected to be present in the cases with KRAS mutation. In addition, a review of 25 studies comparing immunohistochemistry (IHC) using the anti-BRAF V600E (VE1) antibody with BRAF V600E molecular testing in 4041 patient samples was included. One-hundred and twenty cases with/without KRAS or BRAF mutations were acquired. The tissue were immunostained with anti-BRAF V600E (VE1) antibody with OptiView DAB IHC detection kit. The KRAS mutated cases with equivocal immunostaining were further evaluated by Sanger sequencing for BRAF V600E mutation. Thirty cases with BRAF V600E mutation showed unequivocal, diffuse, uniform, positive cytoplasmic staining and 30 cases with wild-type KRAS and BRAF showed negative staining with anti-BRAF V600E (VE1) antibody. Out of 60 cases with KRAS mutation, 56 cases (93.3%) were negative for BRAF V600E mutation by IHC. Four cases showed weak, equivocal, heterogeneous, cytoplasmic staining along with nuclear staining in 25–90% of tumor cells. These cases were confirmed to be negative for BRAF V600E mutation by Sanger sequencing. Overall, IHC with anti-BRAF V600E (VE1) antibody using recommended protocol with OptiView detection is optimal for detection of BRAF V600E mutation in CRC. Our data are consistent with previous reports indicating that KRAS and BRAF V600E mutation are mutually exclusive.
Highlights
Colorectal cancer is the third most common cancer and the fourth most prevalent cause of death in the world [46]
Many studies have indicated that BRAF V600E mutation occurs only in tumors that do not carry mutations in KRAS gene and it is widely accepted that these two mutations are mutually exclusive [10, 23, 25, 30]
Out of 60 colorectal cancer (CRC) cases with KRAS mutations 56 cases were scored as negative for BRAF V600E mutation
Summary
Colorectal cancer is the third most common cancer and the fourth most prevalent cause of death in the world [46]. 35–45% of patients with colorectal tumors have mutation in KRAS gene, while BRAF V600E mutation is found in about 5–15% of colorectal adenocarcinomas [8, 9, 26, 31]. Both these mutations are considered to be oncogenic driver mutations, since they are both responsible for the initiation and maintenance of the tumor [10]. The most common of these mutations, the V600E mutation, occurs in exon 15 and results in a substitution from valine to glutamic acid at position 600 within the BRAF kinase domain
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