system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: I read on the cancer research UK website that cancer of the heart is very rare. Does anyone know why this is?
gpt
Cancer at its base is a disease where a cell divides and forgets to stop.  Every time an individual cell divides there is a chance it becomes cancerous.  The cells in the heart divide significantly less often then other areas of the body.  So there are fewer opportunities for a cancer cell to start.