The goal of this observational study is to screen and differentiate common cancers in participants with or without suspicious lesions. The main question the investigators aim to answer is: Can the developed model, using peripheral blood cell-free DNA sequencing, work well in screening and classifying common cancers especially in the early stages? Participants will undergo the collection of 15~20ml of blood and 1~2 telephone follow-up calls.

Inclusion Criteria:

1. >20 and < 80 years old.
2. Cancer group: Newly diagnosed cancer patients with a confirmed pathological diagnosis within 90 days before blood collection or within 30 days after blood collection, including lung cancer, esophageal cancer, breast cancer, stomach cancer, colorectal cancer, liver cancer, and pancreatic cancer.

Non-cancer group: Individuals who have not been diagnosed with cancer during routine physical examinations and one-year follow-up.

Exclusion Criteria:

1. Uncontrolled or active systemic diseases, such as autoimmune diseases, tuberculosis, AIDS, etc.
2. New onset, recurrence, or exacerbation of various inflammations within 2 weeks before blood collection, or the presence of fever, use of corticosteroids.
3. New onset or exacerbation of thromboembolic diseases, hemorrhagic diseases, or those who have received allogeneic blood transfusion within 1 month before blood collection.
4. Any cancer treatment performed within the past 3 years.
5. Individuals who have undergone organ or bone marrow transplantation.
6. Participants during pregnancy or lactation.
7. Individuals with malnutrition, severe mental illness, or genetic diseases.
8. Other diseases or conditions deemed by the physician as unsuitable for participation in this study.
9. Individuals who are unable to sign an informed consent form.

PASS 21.0 is used to calculate the sample size for diagnostic tests. Based on the specificity and sensitivity of different cancer diagnoses in current and reported studies, the specificity is preset at 98%, and the sensitivity is preset at 75%. A two-sided test is chosen, with a confidence level of 1-α=0.9, and a confidence interval width of 10%. The minimum sample size for the diagnostic test is calculated as follows: each type of cancer should have no less than 202 cases in the diagnostic test, and the total number of cancer subjects should not be less than 1414. The ratio of cancer subjects to non-cancer subjects is set at 1:1. Considering the possibility of loss to follow-up, unqualified sample quality, and dropout during the study, the sample size for this study is preset at 3200.