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There is a verge that is going to be crossed for cancer soon. The reason that cancer research and development is a slow, expensive, ugly morass is that 99% of the people involved are targeting biochemistry peculiar to a very small number of the thousands of relevant varieties and subtypes of cancer. A year of lab time is much the same ballpark of cost whatever you happen to be doing, give or take. So if it takes a thousand distinct cures to defeat cancer, it'll never get done. BUT. There are range of new approaches to cancer that are not particular and specialized to a very small number of cancers, or that can in principle be adapted with comparatively little work to target different cancer types from a common core platform. This is what will produce meaningful control of cancer: attacking the commonalities present in many or all cancer types. The best and most promising approach here is interdiction of telomere lengthening. All cancers must lengthen telomeres. They have to. If they can't, they wither. So block telomerase, block ALT, and cancer goes away. You can either block these mechanisms globally for a while, long enough to kill the cancer, but not long enough to kill the patient due to stem cell depletion, or combine this with any of the targeted delivery mechanisms under development to turn it off only in cancer tissue. There are a few labs working on aspects of this, more on the telomerase side ( e.g. http://www.eurekalert.org/pub_releases/2015-05/cndi-csa05111... ) than the ALT side, because ALT cancers are only about 10% of the total, and ALT is still not completely cataloged. ( See: http://www.the-scientist.com/?articles.view/articleNo/42444/... ) SO. It is foolish to talk about cancer as a thing that medical science cannot get to the bottom of. There are very clear approaches to get to the bottom of cancer and fix it. |
Reason 1; cancer therapies have to effectively kill cancer cells and not important non-cancer cells. Cancer therapies that exist today achieve this by mucking about in mechanisms that are important to cancers and not (or not so much) to other cells. But cancers are diverse- there may just not be anything that's common to all cancer and not shared by healthy cells. Telomere regeneration is a nice candidate, but as you noted, its also important to stem cells- can humans withstand enough damage to their stem cell populations to make a meaningful difference to difficult cancers? (For that matter, telomere regeneration is also important to gametes, so telomere-based therapies may also render the patient infertile.)
Which means we're likely to be stuck dealing with a dozen or hundred-odd different treatments, each of which targets some eccentricity of a specific cancer subtype, but-
Reason 2: There are lots of smart people plugging away at this problem, backed by lots of research money. In addition to being an objectively important problem for humanity, cancer is also an interesting biological conundrum and also the most likely cause of death for a bunch of old people with stratospheric net worths. Even hacking at the problem in bits and pieces, its not unlikely that cancer will become a completely tractable disease (even if a golden-bullet "cure" doesn't arrive) within our lifetimes.