system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: The Lymph System kills dangerous cells, so why doesn´t it kill cancer cells?
gpt
Immune cells can kill cancer cells. But cancer cells are able to induce local immunosuppression, basically sending signals that tell the immune cells not to attack it. Additionally, cancer cells look very similar to human cells. They can look completely normal to our immune system because they’re still fundamentally human cells. This means that our immune cells see them as normal and won’t kill them or detect them as dangerous for targeting. 

Lastly, cancer cells are heterogenous. A single cancer cell, as it divides, undergoes more mutations. Cells that can’t cope to such a strange environment die. cells that get targeted by immune cells die. Through evolution, the most hardy and, stealthy cells survive.