The goal of this observational study is to learn if cfDNA fragmentomics can noninvasively diagnose whether lung nodules are benign or malignant in adults with imaging-detected lung nodules.

Inclusion Criteria:

• Age ≥ 18 years;
• Positive for lung nodules on low-dose spiral CT (LDCT) meeting one of the following criteria:

Solid or part-solid nodules ≥ 5 mm and ≤ 20 mm; Pure ground-glass nodules ≥ 8 mm and ≤ 30 mm; In cases of multiple nodules, the largest nodule (by maximum diameter) must meet these criteria;

• Participants whose lung nodule status (benign or malignant) can be clinically confirmed;
• No cancer-directed therapy (e.g., chemotherapy, radiotherapy, immunotherapy, cell therapy) within the past 3 months;
• Able to provide a 5 mL peripheral blood sample prior to any treatment;
• Voluntary signing of informed consent after full explanation of the study.

Exclusion Criteria:

• Pregnant or breastfeeding;
• Current or past diagnosis (within the past 5 years) of malignant tumors (excluding patients with early-stage lung cancer who have undergone surgery but still have multiple evaluable nodules), or with severe heart disease, serious liver or kidney disorders, or significant bone marrow hematopoietic dysfunction;
• History of organ transplantation or blood transfusion within the past 3 months;
• History of seropositivity for human immunodeficiency virus (HIV);
• Any other condition deemed inappropriate for study participation by the investigators.

This study will enroll adults (≥18 years old) with CT-detected pulmonary nodules of specified types and sizes, who are willing to undergo diagnostic confirmation and provide a peripheral blood sample prior to treatment. Participants must not have received cancer therapy within the last 3 months.