What is Cancer?

This blog has a single post (this one) dedicated to helping figure out what cancer is.

Rarely in medicine are diseases cured without really understanding the disease, and right now science and medicine is at a standstill on understanding cancer.

It matters not whether you are an MD, a plumber, a patient, or a couch potato; we want you to help.

Please use the comment field (either anonymously or not) and answer the following question:

What is cancer (in one sentence or less)?