To understand why lung cancer patients have fever, let’s first understand what fever is. Fever is also called fever by the people. Fever is mainly caused by the effect of thermogenic source to move up the body temperature regulating point and thus causing a regulatory body temperature increase. According to the temperature status, fever is divided into: low fever: 37.3 ~ 38 ℃; moderate fever: 38.1 ~ 39 ℃: high fever: 39.1 ~ 41 ℃; ultra-high fever: 41 ℃ or more. There are many causes of fever, the most common being infection (including bacterial infection, viral infection, mycoplasma infection, etc.), followed by connective tissue disease and malignant tumor, etc. The main causes of fever in lung cancer are as follows: 1. obstructive pneumonia caused by tumor obstruction and poor drainage of bronchial cavity, which can be treated with antibiotics and the body temperature can be restored to normal, but it is easy to recur 2. fever caused by necrosis of tumor cells and release of inflammatory mediators, which is also called tumor fever in clinical practice, and the body temperature is usually below 38°. For older male smokers, they should be alert to the possibility of lung cancer if they have long-term fever and the anti-inflammatory treatment is not effective.