Background BRAF mutation has been recognized as an important biomarker of colorectal cancer (CRC) for targeted therapy and prognosis prediction. However, sequencing for every CRC case is not cost-effective. An antibody specific for BRAF V600E mutant protein has been introduced, and we thus examined the utility of BRAF VE1 immunohistochemistry for evaluating BRAF mutations in CRC.
Methods Fifty-one BRAF-mutated CRCs and 100 age and sexmatched BRAF wild-type CRCs between 2005 and 2015 were selected from the archives of Asan Medical Center. Tissue microarrays were constructed and stained with BRAF VE1 antibody.
Results Forty-nine of the 51 BRAF-mutant CRCs (96.1%) showed more than moderate cytoplasmic staining, except for two weakly stained cases. Six of 100 BRAF wild-type cases also stained positive with BRAF VE1 antibody; four stained weakly and two stained moderately. Normal colonic crypts showed nonspecific weak staining, and a few CRC cases exhibited moderate nuclear reactivity (3 BRAF-mutant and 10 BRAF wild-type cases). BRAF-mutated CRC patients had higher pathologic stages and worse survival than BRAF wild-type patients.
Conclusions BRAF VE1 immunohistochemistry showed high sensitivity and specificity, but occasional nonspecific staining in tumor cell nuclei and normal colonic crypts may limit their routine clinical use. Thus, BRAF VE1 immunohistochemistry may be a useful screening tool for BRAF V600E mutation in CRCs, provided that additional sequencing studies can be done to confirm the mutation in BRAF VE1 antibody-positive cases.
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Mutations in the p53 gene occur during the development of colorectal carcinomas, and play an important role in the conversion of adenoma into carcinoma. To detect the p53 gene mutation and its pattern of expression in colorectal carcinomas, polymerase chain reaction for exons 5, 6, 7, and 8, recombinant gene cloning, and automated DNA sequencing were performed with 30 fresh colorectal carcinomas. Each tissue was also analyzed by immunohistochemical staining for p53 protein.
p53 protein was detected in 25 of 30 (83.3%) colorectal carcinomas by immunohistochemical study. p53 mutation was detected in 4 of 30 (13.3%) colorectal carcinomas. The distribution of these mutations among these exons investigated was as follows: Three mutations in exon 5 (66.7%) and 1 mutation in exon 7 (33.3%). One case with mutation in exon 5 had mutations at three different codons. Mutations in exon 5 were found at codon 153 (GGG to AGG: Gly to Arg), 170 (TGC to GGC: Cys to Gly), 186 (CTA to TTA: silent mutation), 158 (GCG to ACG: Ala to Thr), and 176 (ACG to ATG: Thr to Met). Mutation in exon 7 was found at codon 248 (AGG to AGA: silent mutation). Four of them were missense mutations.
Two of 6 mutations were silent mutations. Five transition mutations and 1 transversion mutation were also detected. All cases with mutations by automated DNA sequencing showed positive p53 protein immunohistochemical stainining.
In conclusion, p53 gene mutation was detected in 4 of 30 (13.3%) colorectal carcinomas, located in codon 153, 158, 170, 176, and 186 of exon 5 and codon 248 of exon 7.
Further studies are needed to evaluate the significance of the codon 153 mutation which was not recognized in other studies on colorectal carcinomas.