system
Given the following post, respond as if you're commenting on Reddit:
human
Why does cancer appear so many years later?

The toxic dust from 9/11 caused hundreds/thousands of cancer cases every year. 
If the cancer cases happened a year or two after the initial exposure I’d understand. But why are they so latent/dormant for so many years? Is it because the dust was just ‘sitting’ in their lungs doing damage over years?
gpt
Here is a simplistic general explanation: 

Our bodies immune system and other mechanisms  is responsible for clearing any abnormal cells, that includes cells that turn cancerous, you could have cancerous cells form I. Your body everyday but as long as the immune system clears then you are good.

Carcinogenic stuff, work by causing mutations in the cells that replicate as part of the normal life cycle of each cell, the more carcinogenic compounds you have, the more mutations or mistakes happen in the replication process. These mistakes result in abnormal cells the immune system recognize them and kill them.

But the immune system also have mechanisms that temper its zeal, if it gets exposed to a substance long enough, it starts to ignore it sometimes, or react in a less aggressive manner. This is an important feature of the immune system, because without it, you will just develop stronger and stronger reactions to everything you get exposed to. People with autoimmune problems have reactions that are not being controlled properly. 


When some one has been exposed to carcinogenic stuff long enough, as well as general aging process. overtime the cells will develop more mutations, eventually creating a cell line with just enough mutation to become cancerous but without anything that triggers the immune system properly, and also, the immune system gets to see these kinda mutations frequently enough it starts to treat them like self antigens and starts ignoring them. This makes for the correct circumstances for a cancer to start actually growing without being checked by the body, and the person now have an actual cancer.