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Heterogeneous distribution of K-ras mutations in primary colon carcinomas: implications for EGFR-directed therapy
Satu Oltedal1, Ole Gunnar Aasprong, Jannicke H Møller
1Laboratory for Molecular Biology, Stavanger University Hospital, PO Box 8100, 4068, Stavanger, Norway.
Purpose:
K-ras mutations predict resistance against epidermal growth factor receptor (EGFR)-directed therapy of metastatic colorectal cancer (CRC). The purpose of this study was to analyze the distribution of K-ras mutations in primary tumors and corresponding sentinel lymph nodes (SLNs) from colon cancer patients.
Methods:
Tumor biopsies and SLNs from 158 patients with non-metastatic colon cancer were analyzed for K-ras mutations in codons 12 and 13 by a sensitive and quantitative peptide nucleic acid clamp PCR assay.
Results:
Analyses of single fresh-frozen tumor biopsies revealed K-ras mutations in 67 (42%) of the patients. Apparently low levels of K-ras mutations in 13 of the mutated primary tumors and the presence of K-ras mutations in SLNs from seven patients with a wild-type primary tumor biopsy suggested possible intratumoral heterogeneity for 20 of the patients. To confirm this hypothesis, we analyzed tissue sections from all available formalin-fixed, paraffin-embedded (FFPE) tumor blocks from these 20 patients. Ten of the patients had a mixture of tissue sections positive and tissue sections negative for K-ras mutations, two patients had K-ras mutations in all sections, and eight patients had no detectable K-ras mutations in tumor FFPE tissue blocks. Among these eight patients, five had K-ras mutations detected in SLNs. Thus, evidence supporting a heterogeneous distribution of K-ras mutations was obtained for 15 patients.
Conclusions:
Heterogeneous distribution of K-ras codon 12 and 13 mutations within primary tumor, or between primary tumor and lymph node metastases, was demonstrated for 15 (20%) of 74 colon cancer patients having K-ras mutations. This may have implications for tissue sampling routines with regard to EGFR-directed therapy of CRC, both in adjuvant and metastatic settings.
Insights
K-ras mutations show heterogeneous distribution in colon cancer primary tumors and lymph nodes. This finding impacts tissue sampling for epidermal growth factor receptor-directed therapy in colorectal cancer (CRC).
Area of Science:
- Oncology
- Molecular Biology
- Genetics
Background:
- K-ras mutations are key predictors of resistance to epidermal growth factor receptor (EGFR)-targeted therapies in metastatic colorectal cancer (CRC).
- Understanding the distribution of these mutations is crucial for effective treatment strategies.
Purpose of the Study:
- To investigate the distribution patterns of K-ras mutations in primary colon tumors and their corresponding sentinel lymph nodes (SLNs).
- To assess the potential for intratumoral heterogeneity of K-ras mutations.
Main Methods:
- Analysis of K-ras mutations in codons 12 and 13 using a sensitive peptide nucleic acid clamp PCR assay.
- Examination of both fresh-frozen tumor biopsies and formalin-fixed, paraffin-embedded (FFPE) tissue sections.
- Inclusion of sentinel lymph nodes (SLNs) in the mutation analysis.
Main Results:
- K-ras mutations were detected in 42% of primary tumor biopsies.
- Evidence of heterogeneous K-ras mutation distribution was found in 15 out of 74 (20%) patients with detectable mutations.
- K-ras mutations were identified in SLNs even when the primary tumor biopsy showed wild-type status, suggesting metastatic spread of mutated clones.
Conclusions:
- A heterogeneous distribution of K-ras mutations exists within primary colon tumors and between primary tumors and lymph node metastases.
- These findings highlight the importance of comprehensive tissue sampling for accurate K-ras mutation status determination.
- The observed heterogeneity has significant implications for guiding EGFR-directed therapy decisions in both adjuvant and metastatic settings for CRC patients.
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