This type of discoloration could be the result of number of factors and not necessarily be precancerous condition. There are few signs which you need to observe like has it changed its color or shape in recent days, is it changing the sensation of tissues around,is it on the cheek outside or inside surface or both, does the tooth touches that area while chewing or at rest etc...a thorough clinical examination with history is required. In case you happen to have any tobacco related habits then get a second opinion too and at the earliest. Be safe then sorry.
Next Steps
Look for a specialist dentist in his area/city. Specialist would have MDS in oral medicine and diagnosis. (There are almost 9 specialty in dentistry and all MDS are not your condition specific as of now)
Health Tips
Don't mention Cancer...let the dentist decide. Sometimes dentists being a human has a one track mind and you mentioning the word might change his diagnosis.