The other thing I found out about life expectancy statistics, is they are mainly guess work. 30 years ago, the chemo they had was completely ineffective against follicular lymphoma. For grade 1, without treatment, the average life expectancy is 12.5 years. So right now they barely have enough statistics to estimate life expectancy for the drugs used 20 years ago. The current set of drugs they use double the average length of remission for high grade lymphomia. There has not been time to adequately study the effects on low grade lymphomia.
However, doubling the length of remissions does not mean doubling your life expectancy. There are two competing factors. Doubling the length of remission means it is more likely the same treatment will work again. In that case double the length of remission could more than double your life expectancy. However, the decease that counts against you is the time you spend out of remission, and that time has not been reduced. So your life expectancy could have changed just a little with the modern drugs, or it could have been extended all the way to a normal life expectancy. Nobody really knows, all you have is guess work.
With advancements in drugs and genetics, I expect in 20 years time they will be able to cure 90% of all cancers. So if they can keep me alive until then, I likely be cured.
So I say, plan for the worst, but live for the best.