###Human: Can blood in sputum be due to cancer in a chronic smoker? ###Assistant: Hello. It is unlikely to be lung cancer. Firstly, the lung cancer is unlikely at this age group and frequently develop after 45 to 50 years. Next thing, blood should have been present consistently and other symptoms would have been present. Most of the times such occasional bleeding is due to mucosal bleeding in mouth or GIT. However, it is better to get evaluated once and get chest X-ray, although unlikely. So, try to convince him.