Methylation is a chemical modification that adds methyl (CH3) groups at selected sites on protein, DNA, and RNA. In humans, DNA methylation only affects the cytosine base (C) when it is followed by a guanine (G). These Cytosine phospho Guanine(CpG) dinucleotides present throughout the human genome at very low frequency except in small areas called CpG islands where CpG content is much higher. Most CpG islands have been observed in the 5′ promoter regions of genes. When promoter CpG islands become methylated, the associated gene is silenced.
The CpG island methylator phenotype (CIMP), characterized by widespread promoter methylation, is associated with microsatellite instability (MSI) and BRAF mutation in colorectal cancer.
- CIMP-high: 3 or more CpG Island loci are methylated
- CIMP-low: 1 to 3 CpG Island loci are methylated
- CIMP-negative: No CpG Island locus is methylated
There are 6 genes in this subgroup of CIMP that is going to be tested: hMLH1; Mint1, Mint2, Mint31; p14, and p16.
PCR-based pyrosequencing of DNA is performed to examine the methylation status of multiple CpG island loci for each of the tested genes. Tumor clone must comprise at least 10% of the cells in the sample.
This assay will detect DNA methylation of CpG island loci for any of the tested genes. The sensitivity of the assay is 10% of methylated DNA in the background of non-methylated DNA.
Formalin-fixed, paraffin embedded tissue blocks containing adequate amounts of tumor to be analyzed (see above sensitivity), with areas to be tested indicated. Comparison of normal and tumor, or several different areas of tumor can be done, for additional charge.
Please provide a copy of the corresponding pathology report.
Additional charges may apply for tissue extraction.
The CPT codes provided are based on AMA guidelines and are for informational purposes only. CPT coding is the sole responsibility of the billing party. Please direct any questions regarding coding to the payer being billed.