Just think that a group of people go out together and eat something bad. Who is more healthy to react to this bad food, the first one or the last one?
Obviously it is the first one who is more healthy because he reacts so quickly. His immune system is in such an alert state that as long as something bad is in- taken, body reacts at once.
Imagine those who do not react at all, are they healthy or they are just numb? Their immune system is so blunt. Why? Because energy level of body is so low.
With that, it is not so hard to understand why nearly all the cancers are found in the later stage because body has not the energy to let you know, your body is not sensitive anymore.