[chimeracoder]

HIV and cancer are particularly tricky.

HIV mutates incredibly quickly, which makes it incredibly hard to find a "vaccine", because something that works against one strain probably won't work against the others. The same goes for treatments - most HIV patients have to take a various combinations of drugs (the slang term is their "cocktail") which vary in effectiveness both per-patient and over time.

Cancer is difficult for a different reason altogether: it's the body's own cells. To oversimplify, it's (relatively) easy to find a medicine that can target foreign cells, but it's hard to find a medicine that will target cancerous cells and not be equally deadly (or more deadly) to healthy cells, because cancerous cells so closely resemble healthy ones.

Progress is being made - just look at Bill Gates and his campaign for eradicating polio.

[gus_massa]

Another problem with cancer is that is not a single illness, but a family of diseases covered with a single name. Bone cancer is very different of pancreatic cancer that is very different from lung cancer that is very different from colon cancer that is very different from ... Some cure approaches work with all of them, but other approaches are more specific. Trying to eradicate all forms of cancers is like trying to eradicate all bacterial diseases at once.

[ekianjo]

Yes and No. You/We should not classify the cancers by "locations". It makes as much sense as classifying a leak in the house as "bathroom leak", "ceiling leak", "stairs leak". There are different cancers happening in different locations of the body and some share the same roots no matter where they start. The fact that they affect a specific organ is not necessarily related to the cancer type itself. There are often several mutations even for a single "cancer location" identified.

[gus_massa]

You are right, I was oversimplifying. For example, Wikipedia lists 4 more frequent types of brain tumors, and each of them has subclassifications. The origin of the cancer is important, because the cancer cell retain some properties of the original cells, for example if they are affected by hormones. So location is important to distinguish if it started as a breast or skin cancer, but it's not important to distinguish if it started as a hand or foot cancer.

(After metastasis, the location is not important to understand the properties of the tumor, but it can affect the symptoms.)

[revelation]

We need to get deeper. Cancer is a direct result from genetic mutations, the very mechanism that enables evolution. It's a (or rather many) mutation that causes uncontrolled cell division while suppressing apoptosis and other mechanisms of the body to regulate cell growth.

(See also: http://en.wikipedia.org/wiki/P53)