According to epidemiological studies, smokeless tobacco products are attributable for 100-200 oral cancer deaths annually in the US. Since modern smokeless tobacco products contain/emit significantly fewer nitrosamines than smokeless products consumed decades ago (which the epi studies evaluated), it is likely that the number and rates of oral cancers associated with smokeless has been and will continue declining.
The CDC estimated that 3,686 of 4,973 (74%) male oral cancer deaths annually in the U.S. from 1997 through 2001 were attributable to cigarettes.
Annual Smoking-Attributable Mortality, Years of Potential Life Lost, and Productivity Losses --- United States, 1997—2001. MMWR July 1, 2005 / 54(25);625-628, CDC, U.S. DHHS.
Annual Smoking-Attributable Mortality, Years of Potential Life Lost, and Productivity Losses --- United States, 1997--2001
The CDC also estimated that 303 (6%) of male oral cancer deaths in 2001 were attributable to alcohol.
Alcohol-Attributable Deaths and Years of Potential Life Lost --- United States, 2001, MMWR, September 24, 2004 / 53(37);866-870, CDC, U.S. DHHS.
Alcohol-Attributable Deaths and Years of Potential Life Lost --- United States, 2001
Thus, the CDC has estimated that 3,989 of 4,973 (80%) of male oral cancer deaths in this country are due to cigarettes or alcohol.
According to the National Cancer Institute (NCI), risk factors for oral cancer include cigarettes, alcohol, cigars, pipe tobacco, SLT, past history of head or neck cancer, and sun exposure.
Oral Cancer, Whose at Risk?, What You Need To Know About Oral Cancer, NCI, 2004.
What You Need To Know About Oral Cancer - National Cancer Institute
Other studies suggest that human papillomavirus (HPV) and not eating enough fruits or vegetables also may be risk factors for oral cancer.
Human Papillomavirus Tied to Oral Cancer, Reuters Health, J Natl Cancer Inst 2003;95:1772-1783.
http://ctep.cancer.gov/resources/gcig/news121003.html
And as pointed out above, a significant percentage of oral cancer victims had no risk factors.