The appearance of high-density shadow on the left side of the lung is a pathological change of imaging manifestation, and the examination finding is not necessarily a manifestation of lung cancer. In clinical practice, lung cancer mainly originates from malignant tumors in the epithelial tissues of the lung, which usually include bronchopulmonary cancer and alveolar cell carcinoma. Lung tumors include benign tumors and malignant tumors, benign tumors such as teratoma and malignant tumors. High-density shadows in the lungs also include other benign inflammatory reactions such as inflammatory pseudotumors, caused by pathogenic infections such as Mycobacterium tuberculosis, Staphylococcus aureus, and Klebsiella. Therefore, high-density shadows on the left side of the lung may be inflammation or benign tumors manifesting as lesions on the left side of the lung, not necessarily lung cancer, and require blood tests, PPD tests, and pathological examination of the lesions with high-density shadows on the left side of the lung if necessary.