That in line with my long held and unpopular thought that really our bodies are rife with mutated and somewhat broken colonies of cells. The idea that you have a slow build up of mutations which finally runaway once the tumor has gotten large is probably just one scenario and perhaps much less common than people want to believe. Very possible you have a the right mutation in a microscopic colony of abnormal cells, and it'll start metastasizing right away. Other cells, will maybe form non-invasive and often self-limiting tumors.

And yeah, thyroid cancer and prostate cancers are way way over diagnosed and over treated to no positive effect.