What are the chances of me having throat cancer having dipped for the past 5-6 years?

Increased. Re: chewing/smokeless tobacco, it is difficult to estimate the increased risk of cancer because of the length of time it takes to develop, however 90% of oral cancer is tobacco related. Oral cancer risk is definitely increased, possibly up to 50%. "throat" cancer is also likely elevated, but it is not clear by how much. http://www.cancer.gov/cancertopics/factsheet/tobacco/smokeless#r1.