The number of people who smoke has fallen significantly, but tobacco use remains a factor in a large percentage of cancers.

According to WILX-TV 10, a new report from the Centers for Disease Control links tobacco to 40 percent of all cancers diagnosed in the U.S.

C.D.C. data also shows fewer Americans are smoking. About 20 percent of adults smoked in 2005.  That number fell to 15 percent last year.