Solid nodule 2.6mm in the apical posterior segment of the upper lobe of the left lung, if it is a benign lesion such as pneumonia or tuberculosis, whether it is serious or not should be determined by the progress of the disease; if it is a malignant tumor such as lung cancer, it is more serious. 1. Pneumonia: when lung tissue is infected by inflammation, solid nodules will be found in the posterior segment of the apical lobe of the lung, which is usually not serious and can be cured after regular treatment. 2. Tuberculosis: when Mycobacterium tuberculosis repeatedly stimulates the lung tissues, inflammatory foci will be formed. The disease itself is not serious, but if it is not treated in time, it may develop into more serious complications and affect the lung function. 3. Lung cancer: it is a malignant tumor of lungs, when the tumor gradually increases, solid nodules will be found. The disease is more serious, but early primary lung cancer can prolong the survival period after regular treatment, while it is more serious if it is secondary lung cancer or develops to middle or late stage, and the patient’s life will be in danger at any time. The solid nodule in the posterior segment of the upper lobe of the right lung needs to be analyzed according to pathological biopsy, and treatment should be carried out as early as possible once malignant lesions are detected, so as to avoid deterioration of the disease affecting the survival rate of the patient.