The lesion in the lower lobe of the left lung is not necessarily cancer. It can be a lesion of tuberculosis, lung infection, fungal infection or granuloma, or it can be a tumor metastasis to the lung from other parts of the body, and the exact nature of the lesion can only be diagnosed by pathology. In case of pulmonary infection, cough, yellow sputum, fever and elevated white blood cell count may be manifested, and the lesions in the lower lobe of the left lung will dissipate and be absorbed after anti-infection treatment. Tuberculosis lesions tend to occur in both upper lobes and in the dorsal segment of the lower lobes of both lungs, and anti-TB treatment is effective for six months. Fungal infections often present as cavernous lesions in the lower lobes with fever and blood in the sputum, which can be dissipated and absorbed with antifungal therapy. Granuloma-like lesions can be diagnosed by surgical excision to find chronic inflammatory cells. The lesions in the lower lobe of the left lung can also be partly caused by tumors, but after anti-infection treatment, the lesions increase progressively, and the diagnosis of cancer can be confirmed mainly by a puncture biopsy of the lower lobe lesions to find cancer cells.