What is this Cancer Thing All of a Sudden

As you read this, I have four friends who have been diagnosed with cancer that has metastasized and are under various courses of treatment, usually radiation and chemo.  They range in age from 30 to 60.  None of them have particularly evil habits so far as I know, e.g. no heavy drinkers or smokers or obesity, etc.   Furthermore, 3 of the 4 are close friends of mine, people who I collaborate and interact with.  People I will miss should anything happen to them.  (The other one is a more distant friend, but still a friend).

Of the four, three of the individuals are walking around, and one of them is in a hospice and unable to speak. 

When you were growing up, did your parents, or school, or other institution (church, synagogue, community center, whatever), did anyone happen to mention that your life could be cut short at any time and that you could have your body ripped apart by a legion of vicious and deadly diseases?

Did they mention that you could be of any age when this happens, and that while there are a variety of things you can do to avoid this fate at least in terms of the odds, that ultimately it is up to chance and how your genes feel like mutating.

Also, if you catch it early, in other words, if you worry about things like this all your life and get tested regularly, then you can probably, but not necessarily, extend your life, i.e. increase survivability. But if you fail to worry about these things then it is possible even likely that you will not notice the problems until it is far too late.

It seems to me that this sucks.

I also have two friends who are HIV positive and have been under treatment for years, perhaps a decade. But they seem to be out and about and doing well.

I have also noticed that my friends who leave this world early all seem to be the nicer ones.  The evil people seem to go on forever.   What is going on here?