Autoimmune diseases: healthy immune response :: cancer: ?

Autoimmune diseases happen when a normally healthy immune system attacks the body’s own cells. In the same way, cancer occurs when the body’s own cells grow and divide without the normal checks and balances that keep growth in control. The key idea is that a healthy process becomes harmful when the regulatory mechanisms fail. For example, a single cell that stops responding to growth‑stop signals can keep multiplying, forming a tumor that spreads to other tissues. Thus, cancer can be seen as the loss of the normal restraint on cell growth.