The Bethesda criteria, in their revised form, refer to a set of pathological features used to identify tumors that are likely to exhibit microsatellite instability (MSI). These criteria help in selecting patients who should undergo further MSI testing.
Key Features of the Revised Bethesda Criteria
The revised Bethesda guidelines look for specific features within tumor samples under a microscope. These features are linked to MSI status. Here are the key pathological features:
- Tumor-infiltrating lymphocytes (TILs): The presence of immune cells (lymphocytes) within the tumor tissue.
- Crohn's-like lymphocytic reaction: An abnormal pattern of immune cell infiltration resembling that seen in Crohn's disease, but within the tumor microenvironment.
- Mucinous or signet ring differentiation: This describes the presence of cells that contain a high amount of mucus or cells that have a signet ring appearance due to a large mucin vacuole pushing the nucleus to one side.
- Medullary or undifferentiated and solid growth pattern: Tumors exhibiting this feature lack specialized cell structures and have a more compact, solid appearance.
Why are the Bethesda Criteria Important?
These criteria are significant because they serve as a pre-screening tool for MSI. MSI is a genomic instability caused by defects in DNA mismatch repair genes. Tumors with MSI have different biological behaviors and responses to certain therapies. Therefore, identifying tumors with these features prompts more specific genetic testing to confirm MSI status.
Example of Bethesda Criteria Use
Imagine a pathologist examining a colorectal cancer biopsy. If they observe a significant number of TILs, a Crohn’s-like lymphocytic reaction, and some signet ring cells, this would suggest that the tumor may be MSI-high. Consequently, the patient would be recommended for further MSI testing such as immunohistochemistry (IHC) or polymerase chain reaction (PCR).
Table Summary of Bethesda Criteria
| Criteria | Description | Implication |
|---|---|---|
| Tumor-infiltrating Lymphocytes (TILs) | Presence of immune cells within the tumor | Suggests an immune response often linked to MSI. |
| Crohn's-like Lymphocytic Reaction | Abnormal immune infiltration pattern resembling Crohn's disease | Indicates potential for MSI. |
| Mucinous or Signet Ring Differentiation | Presence of mucus-producing cells or cells with a large vacuole displacing the nucleus. | Can indicate a tumor with a higher chance of MSI. |
| Medullary/Undifferentiated Solid Growth | Tumors lacking specialized structures; solid, undifferentiated pattern. | A particular histological type associated with MSI. |
By utilizing these features, pathologists can effectively identify tumors that may benefit from further MSI testing, guiding treatment decisions and improving patient care. These criteria help streamline the process of identifying patients with MSI and improve the management of their conditions.
