LU-RADS category 4 lung nodules may be the result of early stage lung cancer, but they may also be the result of benign lung disease or more advanced lung cancer. Based on the imaging assessment of the risk of malignancy of lung nodules known as the LU-RADS (Lung Imaging Reporting and Data System) classification, lung nodules can be categorized into categories 0 to 4. Category 4 nodules are suspicious for malignancy and can be further categorized as 4A, 4B, and 4C, where a category 4A nodule has a risk of malignancy ranging from 5 to 15%, and categories 4B and 4C have a >15% likelihood of being malignant. Category 4 lung nodules have a >5% likelihood of being the result of malignant tumors such as bronchopulmonary carcinoma and metastatic lung cancer, but may also be the result of benign conditions such as misshapen tumors, rheumatoid nodules, and pneumonia. Some of the 4 types of nodules caused by lung cancer are in patients with early stage lung cancer and some are in patients with advanced lung cancer. Generally, category 4 lung nodules need to be analyzed according to the specific categories of 4A, 4B and 4C, and chest CT, PET-CT (Positron Emission Tomography), etc., and tissue biopsy should be performed if necessary. Patients are advised to consult a specialist for further examination and treatment as prescribed.