This is a molecular epidemiological investigation aiming to identify microsatellite instability status from circulating tumor DNA in Chinese patients with refractory advanced solid tumors.

This study is conducted in Chinese patients with advanced refractory metastatic solid tumors. A total of 8-10 mL of blood will be collected from eligible patients and used for extracting circulating tumor DNA. Blood-MSI status will be tested based on SPANOM technique developed by 3D Medicines Inc. Shanghai, China. Patients are encouraged to provide tissues collected from progressive disease for tissue-MSI testing (not required for inclusion).

Inclusion Criteria:

1. Male or female, age≥18 years old.
2. Confirmed malignant solid tumor by histopathology or cytopathology.
3. Colorectal cancer: progression after second-line therapy. Non-colorectal cancer: progression after first-line therapy.
4. Time duration from the last time of anti-cancer treatment to blood sample collection for MSI testing ≥ two weeks or five times half-life period of anti-cancer drugs
5. Signed the informed consent with name and time.

Exclusion Criteria:

1. Hematological malignancy
2. Patients who received immuotherapies.
3. Patients who received blood transfusion within one month before blood collection.
4. Pregnancy.