How long have people known about lung cancer?

Since before 1900: Before the 1900s lung cancer was known about but extremely rare. In the early 1900 as tobacco smoking became more common, so did lung cancer. It was only after world war i (where soldiers were given cigarettes) when the link between cigarette smoking and the growing epidemic of lung cancer was made.

Early: Probably as soon as a anatomical dissections were conducted!

Long time: There's a handful of egyptian papyri that deal with medical issues. Mostly they have to do with trauma but bone and female organ cancers were mentioned (or at least suggested). Not sure about lung cancer but it is conceivable they saw some.