What kinds of chemicals are in smokeless tobacco (snuff), that cause cancer?

Pollutants. All of the pesticides, fungicides and herbicides used on the growing tobacco leaves when they go throught the liver are turned into "estrogen-like" compounds resulting in over-estroginized men and women. They also contain heavy metals all of these can cause various forms of cancers.
Tars. Tobacco contains a number of complex organic alkaloids which are together called "tars." many of them are carcinogenic, and either can cause cancer by themselves, or increase the chance in people who have other predispositions to cancer. Since smokeless tobacco remains in the mouth, it is mostly head and neck cancer (mouth, throat, tongue) that occur. Chewing tobacco does the same thing.