I am a one ppw smoker and in my first checkup in 10 yrs a ct revealed a lung nodule of 4mm. what are the chances that this will lead to lung cancer?

Follow-up: Is this new? Anyway, I recommend that your lung nodule be followed with series CT scans by your doctor. It is too small now for diagnostic work-up. Although many lung nodules in people with smoking could be indolent, your risk is certainly there given your age and smoking history. I do not have data to predict such a chance. But I see this a lot in office. This is usually my recommendation.

1 pack/week?: If one ppw means pack per week then your smoking exposure is probably low to moderate. (40 years smoking x 1 pack per week = 6 pack years of smoking) 55 is younger than average for lung cancer. The nodule needs follow up with serial CT scans. But you need to stop smoking now or you will continue to increase your chances of getting lung cancer, or a heart attack, or early impotency.