A normal tumor marker in a lung nodule does not necessarily indicate that it is a benign tumor. The positive diagnostic rate of tumor markers for lung nodules detected from blood is less than 100% and may even be less than about 30%. Early malignant pulmonary nodules, such as small nodules under 1 cm and ground glass nodules, most of these nodules have normal tumor markers. So just from clinical diagnosis, if only the tumor markers of the lung nodules are detected to be in the normal range, it cannot be used as the final diagnosis. In clinical practice, CT, PET-CT, and even biopsy of lung nodules and pathological examination should be performed to clarify the nature of the tumor before the final diagnosis of benign or malignant lung tumor can be made.