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A very low incidence of BRAF mutations in Middle Eastern colorectal carcinoma.

Siraj AK, Bu R, Prabhakaran S, Bavi P, Beg S, Al Hazmi M, Al-Rasheed M, Alobaisi K, Al-Dayel F, AlManea H, Al-Sanea N, Uddin S, Al-Kuraya KS - Mol. Cancer (2014)

Bottom Line: BRAF mutations were significantly associated with right sided tumors (p = 0.0019), MSI-H status (p = 0.0144), CIMP (p = 0.0017) and a high proliferative index of Ki67 expression (p = 0.0162).Our results highlight the low incidence of BRAF mutations and CIMP in CRC from Saudi Arabia.This could be attributed to ethnic differences and warrant further investigation to elucidate the effect of other environmental and genetic factors.

View Article: PubMed Central - HTML - PubMed

Affiliation: Human Cancer Genomic Research, Research Center, King Faisal Specialist Hospital and Research Center, MBC#98-16, P,O, Box 3354 Riyadh 11211, Saudi Arabia. kkuraya@kfshrc.edu.sa.

ABSTRACT

Background: Recent studies emphasize the role of BRAF as a genetic marker for prediction, prognosis and risk stratification in colorectal cancer. Earlier studies have reported the incidence of BRAF mutations in the range of 5-20% in colorectal carcinomas (CRC) and are predominantly seen in the serrated adenoma-carcinoma pathway characterized by microsatellite instability (MSI-H) and hypermethylation of the MLH1 gene in the setting of the CpG island methylator phenotype (CIMP). Due to the lack of data on the true incidence of BRAF mutations in Saudi Arabia, we sought to analyze the incidence of BRAF mutations in this ethnic group.

Methods: 770 CRC cases were analyzed for BRAF and KRAS mutations by direct DNA sequencing.

Results: BRAF gene mutations were seen in 2.5% (19/757) CRC analyzed and BRAF V600E somatic mutation constituted 90% (17/19) of all BRAF mutations. BRAF mutations were significantly associated with right sided tumors (p = 0.0019), MSI-H status (p = 0.0144), CIMP (p = 0.0017) and a high proliferative index of Ki67 expression (p = 0.0162). Incidence of KRAS mutations was 28.6% (216/755) and a mutual exclusivity was noted with BRAF mutations (p = 0.0518; a trend was seen).

Conclusion: Our results highlight the low incidence of BRAF mutations and CIMP in CRC from Saudi Arabia. This could be attributed to ethnic differences and warrant further investigation to elucidate the effect of other environmental and genetic factors. These findings indirectly suggest the possibility of a higher incidence of familial hereditary colorectal cancers especially Hereditary non polyposis colorectal cancer (HNPCC) syndrome /Lynch Syndrome (LS) in Saudi Arabia.

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Example of BRAF gene mutations in CRC. Sequencing traces of cases harboring wild type (A), and V600E (B), D594G (C) and K601E (D) mutations, respectively.
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Figure 1: Example of BRAF gene mutations in CRC. Sequencing traces of cases harboring wild type (A), and V600E (B), D594G (C) and K601E (D) mutations, respectively.

Mentions: Seven hundred fifty seven colorectal cancer cases were analyzed for BRAF mutations and the remaining 13 cases were not interpretable due to insufficient amount of DNA and other technical reasons. Of the 757 cases analyzed for BRAF status, BRAF mutations were observed in nineteen cases and the incidence of BRAF in Saudi colorectal cancer was 2.5%( 19/757) (Table 2). Surprisingly this is among the lowest incidence of BRAF mutations reported in literature (Tables 3 and4). Of these 19 CRC with BRAF mutations, 17 were seen in the V600E type and the other 2 were seen in V594G and V601E (Table 3 and Figure 1). To reconfirm these results and rule out the fact that we were missing any BRAF mutations due to tumor heterogeneity issues, cancer tissue was re-punched from 2-3 different tumor areas and BRAF analysis was repeated on 400 of these 757 samples. Repeat Sanger sequencing did not show any discordance with earlier results and failed to reveal any new cases with BRAF mutation. As shown in Table 2, CRC with BRAF mutations were significantly associated with right sided tumors (p = 0.0019), microsatellite instable MSI-H status (p = 0.0144) and CIMP high phenotype (p = 00017). Of the 19 cases with BRAF mutation, MSI-H, MSI-L and MSS were 6 cases (31.6%), 5 cases (26.3%) and 8(42.1%) cases respectively. The degree of Ki-67 staining as a measure of proliferative index was significantly higher in the BRAF mutation positive CRC group (88.89 ± 12.78) as compared to the BRAF mutation negative group (80.60 ± 25.30, p = 0.0162; Students T test; Additional file1: Figure S1). A statistical trend was noted with presence of BRAF mutation and older age (age > 50; p = 0.0938) and a mutual exclusivity was observed with KRAS mutations (p = 0.0518; a statistical trend was noted). BRAF mutations were not associated with gender, histology subtype, tumor differentiation and Stage.


A very low incidence of BRAF mutations in Middle Eastern colorectal carcinoma.

Siraj AK, Bu R, Prabhakaran S, Bavi P, Beg S, Al Hazmi M, Al-Rasheed M, Alobaisi K, Al-Dayel F, AlManea H, Al-Sanea N, Uddin S, Al-Kuraya KS - Mol. Cancer (2014)

Example of BRAF gene mutations in CRC. Sequencing traces of cases harboring wild type (A), and V600E (B), D594G (C) and K601E (D) mutations, respectively.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4109832&req=5

Figure 1: Example of BRAF gene mutations in CRC. Sequencing traces of cases harboring wild type (A), and V600E (B), D594G (C) and K601E (D) mutations, respectively.
Mentions: Seven hundred fifty seven colorectal cancer cases were analyzed for BRAF mutations and the remaining 13 cases were not interpretable due to insufficient amount of DNA and other technical reasons. Of the 757 cases analyzed for BRAF status, BRAF mutations were observed in nineteen cases and the incidence of BRAF in Saudi colorectal cancer was 2.5%( 19/757) (Table 2). Surprisingly this is among the lowest incidence of BRAF mutations reported in literature (Tables 3 and4). Of these 19 CRC with BRAF mutations, 17 were seen in the V600E type and the other 2 were seen in V594G and V601E (Table 3 and Figure 1). To reconfirm these results and rule out the fact that we were missing any BRAF mutations due to tumor heterogeneity issues, cancer tissue was re-punched from 2-3 different tumor areas and BRAF analysis was repeated on 400 of these 757 samples. Repeat Sanger sequencing did not show any discordance with earlier results and failed to reveal any new cases with BRAF mutation. As shown in Table 2, CRC with BRAF mutations were significantly associated with right sided tumors (p = 0.0019), microsatellite instable MSI-H status (p = 0.0144) and CIMP high phenotype (p = 00017). Of the 19 cases with BRAF mutation, MSI-H, MSI-L and MSS were 6 cases (31.6%), 5 cases (26.3%) and 8(42.1%) cases respectively. The degree of Ki-67 staining as a measure of proliferative index was significantly higher in the BRAF mutation positive CRC group (88.89 ± 12.78) as compared to the BRAF mutation negative group (80.60 ± 25.30, p = 0.0162; Students T test; Additional file1: Figure S1). A statistical trend was noted with presence of BRAF mutation and older age (age > 50; p = 0.0938) and a mutual exclusivity was observed with KRAS mutations (p = 0.0518; a statistical trend was noted). BRAF mutations were not associated with gender, histology subtype, tumor differentiation and Stage.

Bottom Line: BRAF mutations were significantly associated with right sided tumors (p = 0.0019), MSI-H status (p = 0.0144), CIMP (p = 0.0017) and a high proliferative index of Ki67 expression (p = 0.0162).Our results highlight the low incidence of BRAF mutations and CIMP in CRC from Saudi Arabia.This could be attributed to ethnic differences and warrant further investigation to elucidate the effect of other environmental and genetic factors.

View Article: PubMed Central - HTML - PubMed

Affiliation: Human Cancer Genomic Research, Research Center, King Faisal Specialist Hospital and Research Center, MBC#98-16, P,O, Box 3354 Riyadh 11211, Saudi Arabia. kkuraya@kfshrc.edu.sa.

ABSTRACT

Background: Recent studies emphasize the role of BRAF as a genetic marker for prediction, prognosis and risk stratification in colorectal cancer. Earlier studies have reported the incidence of BRAF mutations in the range of 5-20% in colorectal carcinomas (CRC) and are predominantly seen in the serrated adenoma-carcinoma pathway characterized by microsatellite instability (MSI-H) and hypermethylation of the MLH1 gene in the setting of the CpG island methylator phenotype (CIMP). Due to the lack of data on the true incidence of BRAF mutations in Saudi Arabia, we sought to analyze the incidence of BRAF mutations in this ethnic group.

Methods: 770 CRC cases were analyzed for BRAF and KRAS mutations by direct DNA sequencing.

Results: BRAF gene mutations were seen in 2.5% (19/757) CRC analyzed and BRAF V600E somatic mutation constituted 90% (17/19) of all BRAF mutations. BRAF mutations were significantly associated with right sided tumors (p = 0.0019), MSI-H status (p = 0.0144), CIMP (p = 0.0017) and a high proliferative index of Ki67 expression (p = 0.0162). Incidence of KRAS mutations was 28.6% (216/755) and a mutual exclusivity was noted with BRAF mutations (p = 0.0518; a trend was seen).

Conclusion: Our results highlight the low incidence of BRAF mutations and CIMP in CRC from Saudi Arabia. This could be attributed to ethnic differences and warrant further investigation to elucidate the effect of other environmental and genetic factors. These findings indirectly suggest the possibility of a higher incidence of familial hereditary colorectal cancers especially Hereditary non polyposis colorectal cancer (HNPCC) syndrome /Lynch Syndrome (LS) in Saudi Arabia.

Show MeSH
Related in: MedlinePlus