This is from the Mouth Cancer Foundation uk website:

"Tobacco and alcohol are the most important oral cavity and oropharyngeal cancer risk factors. Mouth cancer is largely a lifestyle disease, meaning that the majority of cases are related to tobacco and alcohol use. Approximately 90% of people with mouth cancer are tobacco users. Smokers are 6 times more likely than nonsmokers to develop mouth cancer. Users of smokeless tobacco have a 50 times more likely chance of developing mouth cancer. Statistics show only 6% of head and neck cancer recurrence in patients who stop smoking in contrast to 37% of head and neck cancer patients who continue smoking developing a second cancer. People who stop using tobacco, even after many years of use, can greatly reduce their risk of all smoking related illnesses, including mouth cancer"

But everyone is different. As we all know - this just isn't an exact science unfortunately.
My chemo nurse said that life stlye choices can make a difference as to whether a cancer will reocour. But that would of course depend on the cause of the original cancer.

As a none smoker it frustrates me too to see people playing russian roulette with their health. I'll never understand it. But i respect it's their choice. & if they get cancer as a direct result of their habit. Then that burden is on their shoulders i guess. Maybe thats harsh?