There are several signs that are sometimes obvious that a malignancy is brewing such as constant cough, sputum mixed with blood, weight loss
(very important), GI symptoms such as voimiting or constant sickness. Getting a chest X Ray
is the first investigation, but HRCT is more sensitive and can be done.
The most important thing you must do is STOP smoking
and it does not matter if it is 1 or 20 cigarettes a day. Asthma/COPD is the obvious progression of lung pathology is you continue and finally ends up with cancer in some people.
There is no reliable blood test
for lung cancer
as is there for some other organ-specific cancers so do STOP smoking.