It can, at least in a sense, depending on how you define cancer. If you mean the presence of malignant cells, the immune system detects and destroys these on practically a daily basis before they form tumors. If you mean the presence of a tumor, then it’s a little more open to question because the cancer has, so to speak, a head start and an advantage in number of tumor cells.
The immune system includes at least three anticancer agents: cytotoxic T-lymphocytes, natural killer (NK) cells, and tumor necrosis factor. The first photo below shows two NK cells destroying a cancer cell, and the second shows two cytotoxic T cells doing the same.
These defenses are always working against malignant and precancerous cells and protecting us from tumor growth more than most people realize. The thing is, it’s a battle and they don’t always win. Also, as we get older, these cells become fewer and less effective, which is one of the reasons so many cancers affect older people more than young ones. As we age, however, these defenses go downhill and we become more vulnerable to cancer and other diseases that a younger immune system can fight off. It’s reported that by age 65, we make few or no T cells anymore. Vaccines become less effective in old age for the same reason; they’re meant to stimulate the immune system, and a tired old immune system just can’t respond to them like it used to.[1] “The aging immune system becomes unable to protect against infections and cancer, to allow proper wound healing, and to respond typically to vaccination.”
According to the literature,
“In humans, the thymus atrophies from infancy, resulting in an exponential decline in T cell production with a half-life of ∼16 years.”[2]
“[By] age 65, we are basically unable to make new T cells.”[3]
“The thymus is the largest and most active in neonates and pre-adolescents, afterwards it gradually involutes and ultimately disappears to be replaced by fat in elderly when it weighs 5g. It is not confirmed that adult thymus can produce significant numbers of new T cells.”[4]
Furthermore, there are other factors making us more susceptible to cancer as we get older:
- Our antioxidant systems weaken, making us more vulnerable to DNA damage by free radicals. [see ref. 4]
- We accumulate more uncorrected mutations simply because of the passage of time;
- Our DNA damage response (DDR) become less effective at repairing mutations. It’s said that them DNA of an average mammalian is damaged 10,000 to 100,000 times per day! Normally our DDR keeps pace with most of this, but less and less as reach old age.
On the other hand, cancer rates go down in the very old (95 to 100+ years old), apparently because these survivors have unusually strong defenses.
In fiurther support:
E. Montecino-Rodriguez et al. 2013. Causes, consequences, and reversal of immune systen aging. *Journal of Clinical Investigation.* 123(3):958–965. Causes, consequences, and reversal of immune system aging (https://www.jci.org/articles/view/64096)
D.B. Palmer. 2013. The effect of age on thymic function. *Frontiers in Immunology*. The Effect of Age on Thymic Function (https://www.frontiersin.org/articles/10.3389/fimmu.2013.00316/full)
S. Palmer et al. 2018. Thymic involution and rising disease incidence with age. *PNAS (Proceedings of the National Academy of Sciences) *115(8):1883–1888. https://doi.org/10.1073/pnas.1714478115 (https://doi.org/10.1073/pnas.1714478115).
Footnotes
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