Cancer is so awful, but I really don't know how it works or why its so hard to cure.
Cancer is kind of an umbrella term for a group of diseases that involve abnormal cell growth. The cells go out of control and invade the other parts of the body. 
Ohh so is it just hard to near impossible to stop the intrusive cell growth?
Cancer
Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumors, which do not spread. Possible signs and symptoms include a lump, abnormal bleeding, prolonged cough, unexplained weight loss, and a change in bowel movements. While these symptoms may indicate cancer, they can also have other causes. Over 100 types of cancers affect humans.
Tobacco use is the cause of about 22% of cancer deaths. Another 10
age and as lifestyle changes occur in the developing world. The financial costs of cancer were estimated at $1.16 trillion USD per year .
Definitions.
Cancers are a large family of diseases that involve abnormal cell growth with the potential to invade or spread to other parts of the body. They form a subset of neoplasms. A neoplasm or tumor is a group of cells that have undergone unregulated growth and will often form a mass or lump, but may be distributed diffusely.
All tumor cells show the six hallmarks