Lung small cell antigen is generally a non-small cell lung cancer antigen, also known as cytokeratin 19 fragment, and can be elevated in benign lesions such as pneumonia or tumors. 1. Benign lesions: mild elevation of cytokeratin 19 fragment (CYFRA21-1) can be seen in pneumonia, tuberculosis, liver cirrhosis, mastitis, kidney failure and other diseases, which are benign lesions. 2. Tumor: CYFRA21-1 is the preferred tumor marker for non-small cell lung cancer, with high positivity rate in squamous cell carcinoma, which is helpful for typing and differential diagnosis of lung cancer. elevated CYFRA21-1 can also be seen in nasopharyngeal carcinoma, breast cancer, bladder cancer, colon cancer and other malignant tumors. It is usually significantly elevated and persistent. Elevated CYFRA21-1 can be seen in a variety of benign and malignant diseases. It is recommended to consult a specialist, make comprehensive judgment based on clinical manifestations, imaging examinations and other tumor markers, and follow the doctor’s instructions for further examination and treatment.