For what length of time can cancer usually go undiagnosed before death?

It varies: Cancer is not one disease...There are over one hundred different disease, each with a differnt course and length of time before they can kill. I have seen most patients get into serious trouble within one to 2 years if left untreated. Of course some can kill in 3-6 months ( e.g.Blood cancers like acute leukemia), others can take 3-5 years(like breast cancer).