Extreme short of breath. my pulmonary doctor first diagnosed as asthma, then after more tests, says i have copd. how do i know it's not lung cancer?

Need more data: Using a combination of a thorough history of symptoms looking for risk factors and examination and imaging.

Be at peace: Say the same thing to your pulmonologist and he might order t scan of lungs 2nd opinion is worth too. Are you a smoker ? Loosing wt ?

Imagine study: Usually an imaging study - CXR, CT scan of chest - will be able to rule in or rule out a mass lesion that could be cancer.