Ironically I was diagnosed with asthma at 56 after a horrible case of what was likely long-Covid. My pulmo team ordered a CT to rule out other issues and because I was a light former smoker for 15 years (who had quit over 20 years ago). The CT revealed 3 “micro nodules” all between 1-2 mm. (Everything else was fine.) Neither my pulmo or the radiologist were concerned … telling me that micro nodules are exceptionally common. They put my stats into some computer program (age, smoking status, BMI, other general stuff) and told the these little nodules had less that a 1 in 10,000 chance of ever becoming cancerous and they saw no reason for follow-up. 3 years later I’m still here and feeling great. 4 mm is also very small … a follow-up CT seems reasonable.