Many patients with lung cancer have swollen mediastinal lymph nodes, but the swollen mediastinal lymph nodes are not necessarily caused by metastasis. There are two main reasons for the enlargement of mediastinal lymph nodes in lung cancer patients: the first reason is the enlargement of lymph nodes caused by the metastasis of lung cancer tissue to mediastinal lymph nodes. The second reason is that the mediastinal lymph nodes may become enlarged due to the reactive hyperplasia of the lymph nodes caused by lung cancer and the inflammatory changes in the lymph nodes. Once a lung cancer patient has enlarged mediastinal lymph nodes, to determine whether it is due to metastasis or inflammation, a puncture biopsy of the enlarged lymph nodes or surgical biopsy is needed to determine whether the enlargement is due to metastasis or inflammation.