Currently, I am studying the release of microRNAs from tumors into the bloodstream. These are genetic regulating molecules, that circulate throughout the body. Based on what I am finding, I don't think that tumor growth is so much a local battle as it is a global one. Personally, I think tumor wages a battle against the immune system more than anything else. It's just an educated guess, but I think if you could give an 80 year-old the immune system of a 20 year old, their oxidative damage wouldn't be such an issue.
"In fact, I believe that you could induce the same tumorigenic mutations in cells of two individuals, and one would grow a tumor and one would not." What makes you state that? Have there been any studies done to point to this conclusion? Also, your research sounds very interesting. Are you at a university, or a national lab (or elsewhere)?
Well, it would be a difficult thing to accomplish since two individuals can't have genetically similar cells to begin with, but there is plenty of evidence for a role of the immune system to combat/prevent cancer. A very basic example is the use of nude mice for in vivo human tumor models. -If you put a human tumor in a mouse, the tumor will not grow. The mouse's immune system recognizes the foreign cells, and rejects them. In some cases, this can even happen if you use tumor from once species of mouse, and implant it in another. Nude mice are mice that have had their immune system suppressed, and as a result, cross-species tumors can grow in them. IMHO, I think it's a poor model, knocking down the immune system, and then studying tumor growth. Also, more indirectly, some chronic infections can lead to cancer. So an immune system that can't suppress infection leaves you vulnerable. For example, HIV increases your risk of some infection-related cancers. Also, your research sounds very interesting. Are you at a university, or a national lab (or elsewhere)? I work in the research department of a large hospital. My funding comes mostly from agencies such as the NIH. We compete for research funding by writing proposals, and by (hopefully) doing compelling work. Funding is awfully low right now, and has been for the last 8 years or so. It's not an easy field to start a career in atm. We don't value basic research enough in the US, IMHO.