Metastasis

You know when they were testing the atom bomb in New Mexico in the 1950's and the movie crew from The Conqueror was filming nearby
They didn't realize there were all these neutron particles released in the explosions
that got into people's bodies and just hammered away
on their bones and tissues for decades, so the cells mutated and spread
The entire cast eventually died of cancer including John Wayne.
I'm one of those particles. Hammering away. It's a long half life, baby.