I’m not an oncologist, but I review a few research studies relating to oncology every year (for their statistical content) - I’ll share what I’ve picked up, but maybe someone else can chip in more information.
Are we close to finding something that will kill cancer cells only? Well, as I understand it, that depends on what kind of cancer cells you are talking about. There are many different types. Some chemo agents work pretty well against certain types of cancer, but there are other types of cancer that are extremely difficult to kill, or even slow/stop the growth of.
One of the past developments that got people really excited was the creation of drugs that slowed or prevented blood vessels from growing to feed tumors. In theory, this prevented them from growing by not permitting them to increase their food (blood) supply. In reality, these agents weren’t as effective as had been hoped.
A lot of the research studies that I see are simply studies to combine different existing regimens of chemo and/or radiation, in hopes of finding something that will add a couple of months to patients’ remaining lifespans. Whether this is really forward-thinking research that will lead to treatment breakthroughs is up for debate. I’ve seen one or two more recently that dealt with trying to develop a “vaccine” - this was pretty interesting to read about, and it requires the product to be tailored to each patient’s tumor cells. As far as a universal cancer vaccine goes, though, I’m not sure that’s possible, just because there are so many different types of cancer and some may be entirely unique to their hosts.
The only thing that would prevent people from getting cancer would be an agent that prevented changes in their DNA. Cells alter their growth and become tumors because of changes in their DNA. However, some other processes in the human body, like those related to some aspects of immunity, depend on the effects of mutation for effective function. If we look at ways to stop tumor growth after these changes have already taken place, then we’re dealing with either a drug/radiation that kills the cells (hopefully selectively!) or a way to make our immune systems recognize the cells as invaders, and mount an appropriate response.