A supporter recently asked the SENS Research Foundation staff whether the implementation of rejuvenation therapies that follow the SENS model of damage repair would prevent the development of cancer, since cancer is predominantly an age-related disease. Would rejuvenation alone, without any progress towards a comprehensive and effective cure for cancer, be good enough to hold cancer at bay?

It's certainly a good bet that applying rejuvenation biotechnologies to remove, repair, and replace other kinds of aging damage will in some ways make us less vulnerable to cancer. Notably, ablating senescent cells would eliminate the "senescence-associated secretory phenotype" (SASP), which promotes the growth and invasiveness of cancers in several ways, including stimulating early-stage cancer cells to continue replicating, encouraging the growth of new blood vessels needed by cancer cells to supply themselves with fuel and oxygen, and breaking down the physical barriers that prevent them from metastasizing, which is when most cancers become deadly. Also, rejuvenating the aging immune system (by eliminating the dysfunctional T-cells that accumulate with age and rebuilding the atrophied thymus gland) will restore the body's ability to suss out and eliminate cancers as they emerge. But it's also clear that deploying these other rejuvenation biotechnologies won't be enough to eliminate cancer altogether, and that must be our ultimate goal.

First, we already know that cancers can evolve multiple mechanisms to avoid being hit or destroyed by antibodies and immunological factors, and the longer a person lives with proto-cancerous cells (even in the presence of a healthy, young immune system), the longer those cells have to develop ways to evade such an immune system. This is one of the reasons that cancer is an age-related disease, despite the fact that young people can and do certainly get cancer, and despite the fact that many late-life cancers originate with mutations that arise in the body decades earlier. More importantly, perhaps, there is good reason to worry that otherwise-rejuvenated tissues in a body that is still vulnerable to the core processes of cancer may actually become more vulnerable to cancer than they would be under "aging as usual." Consider the following contrasting scientific findings.

On the one hand, it has been shown in animal experiments that when you transplant a pre-formed cancer into an old host, it usually grows more quickly than the same cancer does when transplanted into a young one. This is as you'd expect from things that make the aged host more vulnerable to cancer: senescent cells make it easier for the implanted cancer to take root and spread, and a flagging immune system is less able to root out the invader. On the other hand, when you infect mice with a virus that can cause new cancers to form, it is actually less likely to happen in an old mouse than in a young one - and the tumors that do form grow more slowly, despite the weakened immune system and burden of senescent cells in the older animal. This strongly suggests that something about biological aging itself eventually makes our tissues less prone to forming cancers.

Consistent with this, consider the phenomenon of people (and mice) with mutations in DNA repair genes that cause them to accumulate mutations more rapidly than the rest of us. These people develop an "old" burden of potentially cancer-causing mutations in a body that is otherwise still young. This would be similar to having an otherwise-rejuvenated body in which the problem of age-associated mutations had not been solved by a specific rejuvenation biotechnology. Such people develop what are often very aggressive cancers at much younger ages than is typical in the general population. This suggests that once the mutations needed to form a cancer take hold, even an otherwise-young body is unable to hold the invasion back. Thus, rejuvenating the body will reduce the risk of some cancers (notably, by reversing immunosenescence, clearing out senescent cells, and restoring the structural integrity of the extracellular matrix of our tissues). In other ways, however, rejuvenation could restore the host tissues' intrinsic vulnerability to forming new cancers, and to that extent make cancer more of a risk: all those fresh, proliferation-competent cells, and a restored signaling environment full of growth factors.