Polymerase chain reaction (PCR) and subsequent fragment analysis of paired normal and tumor tissue is used to determine microsatellite instability (MSI). Results are reported as MSI-H (at least two markers are unstable) or MSS (less than two markers are unstable).
disease state indication(s)
Colorectal Cancer (CRC)
Predictive, prognostic NCCN Guidelines and a panel of oncology/pathology associations recommend testing for mismatch repair/microsatellite status in all patients diagnosed with colorectal carcinoma. dMMR / MSI-H tumors may respond to immune checkpoint inhibitors such as anti-PD-1 monoclonal antibodies. In comparison to patients with MS-stable (MSS) tumors, MSI-H patients have lower recurrence rates and improved survival, with a more significant effect seen in stage II compared to stage III tumors. Patients with stage II disease with evidence of dMMR or MSI-H may not benefit from adjuvant therapy. Tumors with deficient MMR protein expression (dMMR) or high microsatellite instability (MSI-H) should be tested for BRAF mutation to assess the likelihood of Hereditary Non-Polyposis Colorectal Cancer / Lynch Syndrome (HNPCC/LS).
Polymerase chain reaction (PCR)
specimen type and requirements
Preferred: Two (2) formalin-fixed, paraffin-embedded (FFPE) blocks: one containing tumor tissue from the most recent surgery or biopsy and the other containing normal tissue.
Alternatively, peripheral blood can be used for normal tissue.
Acceptable Alternative: Seven (7) unstained slides at 2×5 µm thickness containing tumor, and seven (7) unstained slides at 2×5 µm thickness containing normal tissue, plus accompanying H&E slides.
Unacceptable: Specimens preserved in alternative (non-formalin) fixatives, decalcified specimens, fresh or frozen tissue.
Note: Use refrigerated cold pack for transport. Make sure cold pack is not in direct contact with specimen.
DO NOT FREEZE.
Global (TC & PC): 7 days
medicare moldx cpt code
Laboratory developed test (LDT)
Global (TC & PC)