This is the single strongest risk factor for developing cancers of the head and neck. Any form of tobacco taken through the mouth, whether smoked or chewed, increases the risk over time. The more tobacco that is used, for a longer period of time, the higher the chance is to get cancer. Likewise, when use is stopped, the risk declines to normal over a 5 to 10 year period. Viruses can also get into the cells of the nose themselves and change the genes in them to form a cancer cell.
Some people seem genetically predisposed to getting cancer from viruses.
This will be especially important in combination with the other risk factors noted. Breathing sawdust and smoke from certain fires increases the risk for nasopharynx and sinus cancers, probably from chronic irritation. A cancer must grow to 1 billion cells to be just 1 cm. As it grows, it produces symptoms in it's local area, and eventually in distant areas as it spreads. When we breathe through our nose, the air then goes into the nasopharynx.