Microsatellite Instability by PCR (MSI)
Microsatellite instability, colon cancer, KEYTRUDA® (pembrolizumab), PCC Screen, MSI Testing, SOFTPATH: MMSIG, SOFT LAB: MMSIG, SOFT GENE: MMSI
Specimen Collection Criteria
Abnormal Tissue: 10% Formalin-fixed, paraffin-embedded tumor block with corresponding H&E slides. Tissue should be well fixed and well processed. Average tissue size 5.0 mm2.
Normal Tissue: 10% Formalin-fixed, paraffin-embedded normal tissue block with corresponding H&E slides. Tissue should be well fixed and well processed. Average tissue size 5.0 mm2. A fresh Peripheral Blood EDTA specimen will be accepted when normal tissue is unavailable.
- DNA will be assessed for quality. If it is deemed unacceptable, testing will be cancelled with client notification.
- The specimen must be accompanied by a completed requisition and must contain the patient name, date of birth, collection date, ordering physician, and source of specimen.
Physician Office/Drawsite Specimen Preparation
Maintain paraffin-embedded tissue at room temperature (20-26°C or 68-78.8°F) until transport.
Preparation for Courier Transport
Transport: Paraffin-embedded tissue, at room temperature (20-26°C or 68-78.8°F).
- Decalcified tissue.
- Fixatives other than 10% neutral buffered formalin.
- Specimens fixed/processed in alternative fixatives (e.g. alcohol, zinc formalin).
- Improper labeling or inadequate information.
- Less than 10 percent tumor cellularity, at discretion of medical director.
- Poor quality and/or quantity of extracted genomic DNA.
Testing will be cancelled on specimens meeting the above criteria with client notification.
Specimen Stability for Testing:
Paraffin-embedded Abnormal and Normal Tissue:
Room Temperature (20-26°C or 68-78.8°F): Indefinitely
Refrigerated (2-8°C or 36-46°F): Unacceptable
Frozen (-20°C/-4°F or below): Unacceptable
Peripheral Blood EDTA:
Room Temperature (20-26°C or 68-78.8°F): 72 hours
Refrigerated (2-8°C or 36-46°F): 72 hours
Specimen Storage in Department Prior to Disposal:
Room Temperature (20-26°C or 68-78.8°F): 7 days
Specimen Storage (DNA post testing):
Frozen (-70 to -80°C): Indefinitely
Royal Oak Clinical Molecular Pathology Laboratory.
Results available in 7-10 days.
Microsatellite stable tumor. Results obtained with tumor DNA are compared with results obtained with the patients normal DNA.
DNA is extracted from the tissue. Primers to six NCI consensus microsatellites are used to amplify both tumor and normal DNA. Fluorescently labeled products are analyzed by capillary electrophoresis. Three additional microsatellite primer sets are used if necessary for clarification of results.
Microsatellite stable, unstable-low (1 unstable locus), unstable-high (2 or more unstable loci).
Detects instability of microsatellite loci associated with a loss or suppression of DNA mismatch repair complex. In colorectal adenocarcinoma, microsatellite unstable-high status can correspond with both sporadic and inherited (i.e. Lynch Syndrome) microsatellite instability, as well as having prognostic implications. Recently, Keytruda was approved by the FDA for use in any solid tumor that is unresectable or metastatic.
Epiphenomenon (i.e. MLH-1 promoter methylation) or heritable colorectal adenocarcinoma MSI conditions (i.e. Lynch Syndrome).
SOFTPATH: MMSIG, SOFT LAB: MMSIG, SOFT GENE: MMSI