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BRAF, KRAS and PIK3CA mutations in colorectal serrated polyps and cancer: primary or secondary genetic events in colorectal carcinogenesis?

Velho S, Moutinho C, Cirnes L, Albuquerque C, Hamelin R, Schmitt F, Carneiro F, Oliveira C, Seruca R - BMC Cancer (2008)

Bottom Line: Chi Square test and Fisher's Exact test were used to perform association studies.Our results show that BRAF, KRAS and PIK3CA mutations occur prior to malignant transformation demonstrating that these oncogenic alterations are primary genetic events in colorectal carcinogenesis.These results support that BRAF mutations harbour a mild oncogenic effect in comparison to KRAS and suggest that BRAF mutant colorectal cells need to accumulate extra epigenetic alterations in order to acquire full transformation and evolve to MSI CRC.

View Article: PubMed Central - HTML - PubMed

Affiliation: Institute of Molecular Pathology and Immunology, University of Porto, Portugal. svelho@ipatimup.pt

ABSTRACT

Background: BRAF, KRAS and PIK3CA mutations are frequently found in sporadic colorectal cancer (CRC). In contrast to KRAS and PIK3CA mutations, BRAF mutations are associated with tumours harbouring CpG Island methylation phenotype (CIMP), MLH1 methylation and microsatellite instability (MSI). We aimed at determine the frequency of KRAS, BRAF and PIK3CA mutations in the process of colorectal tumourigenesis using a series of colorectal polyps and carcinomas. In the series of polyps CIMP, MLH1 methylation and MSI were also studied.

Methods: Mutation analyses were performed by PCR/sequencing. Bisulfite treated DNA was used to study CIMP and MLH1 methylation. MSI was detected by pentaplex PCR and Genescan analysis of quasimonomorphic mononucleotide repeats. Chi Square test and Fisher's Exact test were used to perform association studies.

Results: KRAS, PIK3CA or BRAF occur in 71% of polyps and were mutually exclusive. KRAS mutations occur in 35% of polyps. PIK3CA was found in one of the polyps. V600E BRAF mutations occur in 29% of cases, all of them classified as serrated adenoma. CIMP phenotype occurred in 25% of the polyps and all were mutated for BRAF. MLH1 methylation was not detected and all the polyps were microsatellite stable. The comparison between the frequency of oncogenic mutations in polyps and CRC (MSI and MSS) lead us to demonstrate that KRAS and PIK3CA are likely to precede both types of CRC. BRAF mutations are likely to precede MSI carcinomas since the frequency found in serrated polyps is similar to what is found in MSI CRC (P = 0.9112), but statistically different from what is found in microsatellite stable (MSS) tumours (P = 0.0191).

Conclusion: Our results show that BRAF, KRAS and PIK3CA mutations occur prior to malignant transformation demonstrating that these oncogenic alterations are primary genetic events in colorectal carcinogenesis. Further, we show that BRAF mutations occur in association with CIMP phenotype in colorectal serrated polyps and verified that colorectal serrated polyps and MSI CRC show a similar frequency of BRAF mutations. These results support that BRAF mutations harbour a mild oncogenic effect in comparison to KRAS and suggest that BRAF mutant colorectal cells need to accumulate extra epigenetic alterations in order to acquire full transformation and evolve to MSI CRC.

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Related in: MedlinePlus

KRAS, PIK3CA and BRAF mutation frequencies between MSI/MSS CRC and CR polyps. The frequency of KRAS, PIK3CA and BRAF mutations in MSI and MSS CRC was based on previous results of our group in Velho [10]. In brackets is represented the total of cases that were analyzed for each gene.
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Figure 1: KRAS, PIK3CA and BRAF mutation frequencies between MSI/MSS CRC and CR polyps. The frequency of KRAS, PIK3CA and BRAF mutations in MSI and MSS CRC was based on previous results of our group in Velho [10]. In brackets is represented the total of cases that were analyzed for each gene.

Mentions: In order to understand the importance of KRAS, PIK3CA and BRAF mutations for the progression of the various types of colorectal cancer, we compared the frequency of these oncogenic events in the series of polyps and in 50 MSI and 53 MSS CRC (Figure 1).


BRAF, KRAS and PIK3CA mutations in colorectal serrated polyps and cancer: primary or secondary genetic events in colorectal carcinogenesis?

Velho S, Moutinho C, Cirnes L, Albuquerque C, Hamelin R, Schmitt F, Carneiro F, Oliveira C, Seruca R - BMC Cancer (2008)

KRAS, PIK3CA and BRAF mutation frequencies between MSI/MSS CRC and CR polyps. The frequency of KRAS, PIK3CA and BRAF mutations in MSI and MSS CRC was based on previous results of our group in Velho [10]. In brackets is represented the total of cases that were analyzed for each gene.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2553419&req=5

Figure 1: KRAS, PIK3CA and BRAF mutation frequencies between MSI/MSS CRC and CR polyps. The frequency of KRAS, PIK3CA and BRAF mutations in MSI and MSS CRC was based on previous results of our group in Velho [10]. In brackets is represented the total of cases that were analyzed for each gene.
Mentions: In order to understand the importance of KRAS, PIK3CA and BRAF mutations for the progression of the various types of colorectal cancer, we compared the frequency of these oncogenic events in the series of polyps and in 50 MSI and 53 MSS CRC (Figure 1).

Bottom Line: Chi Square test and Fisher's Exact test were used to perform association studies.Our results show that BRAF, KRAS and PIK3CA mutations occur prior to malignant transformation demonstrating that these oncogenic alterations are primary genetic events in colorectal carcinogenesis.These results support that BRAF mutations harbour a mild oncogenic effect in comparison to KRAS and suggest that BRAF mutant colorectal cells need to accumulate extra epigenetic alterations in order to acquire full transformation and evolve to MSI CRC.

View Article: PubMed Central - HTML - PubMed

Affiliation: Institute of Molecular Pathology and Immunology, University of Porto, Portugal. svelho@ipatimup.pt

ABSTRACT

Background: BRAF, KRAS and PIK3CA mutations are frequently found in sporadic colorectal cancer (CRC). In contrast to KRAS and PIK3CA mutations, BRAF mutations are associated with tumours harbouring CpG Island methylation phenotype (CIMP), MLH1 methylation and microsatellite instability (MSI). We aimed at determine the frequency of KRAS, BRAF and PIK3CA mutations in the process of colorectal tumourigenesis using a series of colorectal polyps and carcinomas. In the series of polyps CIMP, MLH1 methylation and MSI were also studied.

Methods: Mutation analyses were performed by PCR/sequencing. Bisulfite treated DNA was used to study CIMP and MLH1 methylation. MSI was detected by pentaplex PCR and Genescan analysis of quasimonomorphic mononucleotide repeats. Chi Square test and Fisher's Exact test were used to perform association studies.

Results: KRAS, PIK3CA or BRAF occur in 71% of polyps and were mutually exclusive. KRAS mutations occur in 35% of polyps. PIK3CA was found in one of the polyps. V600E BRAF mutations occur in 29% of cases, all of them classified as serrated adenoma. CIMP phenotype occurred in 25% of the polyps and all were mutated for BRAF. MLH1 methylation was not detected and all the polyps were microsatellite stable. The comparison between the frequency of oncogenic mutations in polyps and CRC (MSI and MSS) lead us to demonstrate that KRAS and PIK3CA are likely to precede both types of CRC. BRAF mutations are likely to precede MSI carcinomas since the frequency found in serrated polyps is similar to what is found in MSI CRC (P = 0.9112), but statistically different from what is found in microsatellite stable (MSS) tumours (P = 0.0191).

Conclusion: Our results show that BRAF, KRAS and PIK3CA mutations occur prior to malignant transformation demonstrating that these oncogenic alterations are primary genetic events in colorectal carcinogenesis. Further, we show that BRAF mutations occur in association with CIMP phenotype in colorectal serrated polyps and verified that colorectal serrated polyps and MSI CRC show a similar frequency of BRAF mutations. These results support that BRAF mutations harbour a mild oncogenic effect in comparison to KRAS and suggest that BRAF mutant colorectal cells need to accumulate extra epigenetic alterations in order to acquire full transformation and evolve to MSI CRC.

Show MeSH
Related in: MedlinePlus