The testing itself is an issue as well. Most people think that you put a blood sample in a machine and it spits out "yes you have cancer" or "no you don't", but

The testing itself is an issue as well. Most people think that you put a blood sample in a machine and it spits out "yes you have cancer" or "no you don't", but in reality in the earliest stages it's more akin to reading tea leaves. The chances of false positives are high, and can be equally or more harmful to the patient than false negatives. This is also why doctors are increasingly recommending that young, healthy people not get routine annual checkups and blood work done unless they have any specific problems.