The purpose of this study is to find out the proportion of patients diagnosed with Lynch syndrome in colorectal cacner patients meeting Chinese Lynch syndrome criteria. Besides, this study is aimed to analyze the clinical characteristics and germline mutation of Lynch syndrome in Chinese population.

1. Detect germline mutation (by next-generation squencing) in probands.
2. Verify the germline mutation in blood relatives whose proband has known germline mutation(s).
3. Analyze the test data with clinical and family information. Diagnose Lynch syndrome in the included population.
4. Analyze the clinical characteristics and germline mutation of Lynch syndrome in Chinese population.

For probands, the inclusion criteria： all of the following three points should be satisfied:

1. One of the colorectal cancer patients from families meeting Chinese Lynch syndrome criteria.

   Chinese Lynch syndrome criteria:

   In a pedigree, there were at least 2 patients with histological-proven colorectal cancer, and among these, at least two patients are first-degree relatives of each other. Besides, any one of the following three points should be satisfied in the pedigree:

   A. at least one patients with multiple primary colorectal carcinoma/adenoma, either synchronously or metachronously.

   B. at least one colorectal cancer diagnosed before 50 years old. C. in the pedigree, at least one patient diagnosed with other Lynch syndrome associated cancer (ie, gastric, endometrial, small bowel, ureter, or renal-pelvic, ovarian and hepatobiliary cancers).

2. With sufficient blood to test;

3. Agree to provide basic information, clinical information and family history of cancer information.

For probands, the exclusion criteria:

With at least one blood relative with known pathogenic germline mutation(s).

For blood relatives verifying germline mutation, the inclusion criteria： all of the following three points should be satisfied:

1. First- to second-degree blood relatives of probands with germline mutation(s).
2. With sufficient blood to test.
3. Agree to provide basic information, clinical information and family history of cancer information.

For blood relatives verifying germline mutation, the exclusion criteria:

Blood relatives who refuse to test.

The probands will be selected from colorectal cancer patients meeting Chinese Lynch syndrome criteria. The blood relatives verifying germline mutation will be selected from whose proband has germline mutation(s).