Frequent infectious diseases. Lungs perform an important function in the body, and sometimes various infectious diseases can get into the body through the respiratory system. In chill weather, you can catch a cold or even pneumonia. But if the colds happen 4-5 times a season, despite the full treatment and adjustment of immunity, there is the reason to think about an examination for lung cancer. The malignant formation can block part of the airways, leading to the growth of infection, while preventing the effects of medicament on the damaged area. That is why the viruses of infection do not respond to treatment, and they excruciate patients by frequent relapses.