This publication discusses a number of issues relevant to cancer diagnosis and screening to guide general public health or the scientific community, hence to refine Lynch syndrome - also known as hereditary non-polyposis colorectal cancer (HNPCC) - and microsatellite instability (MSI) was an effort in that direction. Recent findings warrant a re-examination of the current issues and guidelines for HNPCC diagnosis. MSI and immunohistochemistry (IHC) detection are that other molecular tests that have surfaced for detecting DNA mismatch repair (MMR) defects and have not been included in previous HNPCC diagnostic guidelines. This volume aims to generate recommendations on appropriate strategies for evaluating MSI; diagnosing HNPCC; and identifying HNPCC mutation carriers.