Previously, the ACS called for screening only for long-time or heavy smokers who had given up cigarettes less than 15 years earlier.

The new guidance from the influential organization says the need for screening should no longer be determined in part by how much time has passed since smokers quit. 

The ACS says the new guideline applies to anyone who smoked for 20 so-called pack-years, for example, a pack a day for 20 years or two packs a day for 10 years.

The traditional assumption had been that after 15 years of no longer smoking, the risk of lung cancer had dropped to such a low level that screening was no longer cost effective. 

New data show that as former smokers’ lung cancer risk from smoking goes down, their risk of these malignancies from aging goes up, ACS researchers said.