The "3-2-1 rule" refers to a simplified way of remembering some aspects of the original Amsterdam criteria for identifying families with Hereditary Non-Polyposis Colorectal Cancer (HNPCC), now more commonly referred to as Lynch syndrome. The complete rule is sometimes described as the "3-2-1-0 rule," but the core of it involves the numbers 3, 2, and 1. According to the Amsterdam criteria, HNPCC was defined by the following criteria being met:
- 3: Three or more individuals in the family must have pathologically confirmed colorectal cancer.
- 2: Two or more successive generations must be affected.
- 1: One affected family member must be a first-degree relative of the other two.
Note: The reference provided refers to the original Amsterdam criteria. These criteria have since been updated due to their limited sensitivity and the recognition that Lynch syndrome can involve cancers other than colorectal cancer. The revised Bethesda guidelines and subsequent clinical practice rely more heavily on tumor testing for mismatch repair deficiency and microsatellite instability.
