BRAF V600E and Mismatch Repair Proteins Expression in Sporadic Young-onset Colorectal Cancer in Kelantan, Malaysia

Abstract

Objectives: We sought to determine the immunohistochemistry expression of mismatch repair (MMR) and BRAF V600E proteins in sporadic young-onset colorectal cancer (CRC) and their association with clinicopathological features in the Kelantan population.

Methods: This was a cross-sectional study of sporadic young-onset CRC over 11 years from 1 January 2006 to 31 December 2017 in Kelantan. Formalin-fixed paraffin-embedded tissue blocks were immunohistochemically stained with antibodies for MMR (MLH1, MSH2, MSH6, and PMS2) and BRAF V600E. These expressions were correlated with clinicopathological parameters.

Results: Our patient sample included 31 patients with a mean age of 31.5 years. More than half (61.3%) of the patients were women. The majority presented with abdominal pain (41.9%), and 71.0% had a tumor located on the right side of the colon, with 83.9% being moderately differentiated adenocarcinoma. The majority of patients presented at stage IV (54.8%). The most frequent pattern was all MMR protein expressions, which constituted patients in the microsatellite stable group (64.5%). Nine (29.0%) were microsatellite instability (MSI-high), and two (6.5%) were MSI-low. Positive BRAF V600E expression was observed in 83.9% of patients. Only histopathological subtypes revealed a significant association with BRAF V600E positive expression (p = 0.015).

Conclusions: The majority of sporadic young-onset CRC presented with abdominal pain and advanced cancer stage. Most were microsatellite stable, and most cases showed positive expressions in all MMR markers and BRAF V600E by immunohistochemistry method. This finding will pave the way for further research on this disease.

Keywords: Colorectal Neoplasms; Mismatch Repair Endonuclease PMS2; MutS Homolog 2 Protein; Proto-Oncogene Proteins B-raf.

Figure 1

Nuclear intensity scoring for the mismatch repair protein expression (MLH1, MSH2, MSH6, and PMS2).(a) Score 0 (magnification = 100 ×), (b) score 1 (magnification = 400 ×), (c) score 2 (magnification = 400 ×), and (d) score 3 (magnification = 400 ×). The nuclear intensity was compared with the internal positive control (lymphocytes). A score of 3 indicates intensity as strong as the internal positive control.

Figure 2

Representative staining results for the mismatch repair (MMR) protein expression and BRAF mutation through immunohistochemistry. (a) Colorectal sections using an antibody towards the MMR protein showing positive nuclear staining (magnification = 400 ×). (b) Colorectal cancer sections using an anti-BRAF V600E antibody, showing positive cytoplasmic staining (magnification = 400 ×).

Figure 3

Positive control for the anti-BRAF V600E antibody. (a) Melanoma tissue used as positive control showing positive cytoplasmic staining for anti-BRAF V600E antibody (magnification = 400 ×). (b) Positive cytoplasmic staining was observed in the colorectal cancer tissue (magnification = 400 ×). Twenty-six out of 31 patients show positivity towards the anti-BRAF V600E antibody.