Great question and in part, you are correct. However, you must also remember that this greatly depends on what genes have undergone mutation. 

In the case of cancer, it's usually either a gene that regulates cell proliferation rates, induces programmed cell death or helps to repair damaged DNA. When one (or all) of these genes is mutated, the cell constantly proliferates and/or does not die when it is "programmed" to do so or cannot repair mutations to it's DNA, thus creating a cancerous tumor.

Now, on to the immune system. The reason a persons immune system does not target and kill it's own cells is because of a certain set of genes that is specific to each and every person called Major Histocompatibility Complex (MHC). These genes encode specific cell surface molecules that the immune system cannot produce antibodies to bind to because they are "locked", if you will (see, the immune has a sort of built-in list of genes that code for antibodies that bind to different sequences of molecules (that's how you develop immunity and fight pathogens), the genes that code for the specific molecules that your cells have on their surface are just not on that list.) In order for a person's immune system to recognize cancerous cells as a pathogen and destroy them, the cancer cell's MHC genes would also need to be mutated drastically.

For instance, breast cancer is usually caused by a mutation in the BRCA1 or BRCA2 genes. These genes assist in DNA repair. Even if this mutation happens, these cells still have the same MHC as the rest of the cells in your body because BRCA1 and BRCA2 don't really have much to do with MHC. Because of this, the immune system does not recognize the cancerous cells as a threat and is unable to destroy or even detect them.

I hope this answers your question.

CDB

If Tumors have lots of mutations in them how is it the immune system can't detect them?
I have a menu that I've created using jquery that "pops-up" on certain button mouse-overs.

it has a LOT of options and sub-menu options and I'd like to put it into a separate file so that it only needs to be downloaded once and all of the html markup and text doesn't need to be re-downloaded every time a user hits a sub page on my site.

I was toying with the idea of using the jquery template engine but couldn't quite wrap my head around the best way to work that.  This isn't a template after all, but a static menu.

I'm pretty sure I can't put it in a JS file because it's not script per se, it's actual html markup (mostly tables).

Any ideas?
