Cigarettes?  Nah.  Lung cancer is caused by microwaving popcorn:

Consumers, not just factory workers, may be in danger from fumes from buttery flavoring in microwave popcorn, according to a warning letter to federal regulators from a doctor at a leading lung research hospital.

A pulmonary specialist at Denver’s National Jewish Medical and Research Center has written to federal agencies to say doctors there believe they have the first case of a consumer who developed lung disease from the fumes of microwaving popcorn several times a day for years.

"We cannot be sure that this patient’s exposure to butter flavored microwave popcorn from daily heavy preparation has caused his lung disease," cautioned Dr. Cecile Rose. "However, we have no other plausible explanation."

Oh come now!  One guy gets lung cancer and you blame it on popcorn??  And you issue a nationwide alert?

Panic much?