One of the reasons that cancer is overwhelmingly a condition of the old is that the immune system is responsible for eliminating potentially cancerous cells, but declines in effectiveness with age due to a combination of damage and structural issues. The immune system supports a limited number of cells and continually devotes some of those cells to remembering threats - by late in a normal human life space it begins to experience resource issues, overburdened by memory cells and lacking enough naive cells to effectively tackle new threats.
Methods of even partially rejuvenating the immune system, such as implementing portions of the SENS program, or selectively destroying the burden of immune cells uselessly specialized to fight CMV so as to free up space for new and more useful immune cells to emerge, should reduce incidence of cancer in the old.
The research noted here illustrates this point, demonstrating just how important the immune system is to suppression of one particular type of cancer:
Immune cells undergo 'spontaneous' changes on a daily basis that could lead to cancers if not for the diligent surveillance of our immune system. This immune surveillance accounts for [the] 'surprising rarity' of B-cell lymphomas in the population, given how often these spontaneous changes occur.
The discovery provided an answer to why B-cell lymphomas occur in the population less frequently than expected. "Each and every one of us has spontaneous mutations in our immune B cells that occur as a result of their normal function. It is then somewhat of a paradox that B cell lymphoma is not more common in the population. "Our finding that immune surveillance by T cells enables early detection and elimination of these cancerous and pre-cancerous cells provides an answer to this puzzle, and proves that immune surveillance is essential to preventing the development of this blood cancer."
The research team made the discovery while investigating how B cells change when lymphoma develops. "As part of the research, we 'disabled' the T cells to suppress the immune system and, to our surprise, found that lymphoma developed in a matter of weeks, where it would normally take years. It seems that our immune system is better equipped than we imagined to identify and eliminate cancerous B cells, a process that is driven by the immune T cells in our body."