Aging and Cancer
we consider carcinogenesis to be a form of premature aging?
What I'm trying to say here is that sunlight ages skin (The Aging of Skin).
Cigarette smoke ages lung tissue (along with other tissues in the body... viz., skin, bladder, etc.).
It may be that the deleterious effects of carcinogens aren't exactly the same as those brought on by aging, but they're close enough that, perhaps, we can conclude that repeated environmental insults lead to a form of premature aging. As stated in "The Aging of Skin", skin that is protected from sunlight shows almost no signs of aging. Similarly, lungs of non-smokers who aren't exposed to second-hand smoke or radon will probably never be at significant risk of developing lung cancer.
The probability of cancer rises when a cell approaches its proliferative (Hayflick) limit, and quits dividing. When the cell is unable to repair all of its cell damage, it first stops dividing, as a protection against improperly functioning cells, and later, undergoes apoptosis (cellular suicide). Cancer occurs when a cell fails to commit suicide, and, in addition, begins to produce telomerase in a mode unlike that of skin cells. Instead of sequestering telomerase in the nucleus in between cell divisions, as is the case with normal skin cells, a cancer cell produces telomerase continuously, allowing the chaotic recombination of broken strands of chromosomes, and generating a rapid mutation rate.
This is giving me a new perspective on the intimate relationship between cellular aging and the etiology of cancer.
Like aging, carcinogenesis is cumulative, irreversible, and asymptomatic
The meaning of this kind of model is that, like aging, carcinogenesis is cumulative, irreversible (with today's technology), and is usually asymptomatic. Smoking another cigarette causes no pain. If it did, people would be more aware of its dangers. Similarly, improving one's tan is generally painless. It's easy to say to one's self, "Eating one piece of ham or one piece of pizza isn't going to do me a lot of harm", and that's undoubtedly true. It's when one piece of ham leads to three more, or one piece of pizza isn't enough, that we may stray down the primrose path to dalliance. (I hate to brag, but I have a certain expertise in justifying why another piece of pizza or a little more dressing and gravy is really justified.) There's no early warning for cancer, so this puts the onus on us to avoid premature aging even though we don't feel the effects.
Another source of trouble is viral infections with viruses like the herpes virus, the human papilloma virus, the cytomegalovirus, and the hepatitis viruses.
If we could observe hidden tissue, there would probably be such early warning signs as polyps and benign cysts (analogous to actinic keratoses in skin).
We need to know more about the causes of aging and cancer
One of the biggest problems has been, and may still be, that we don't know all we'd like to know about the causes of cancer and aging.
What causes body elements to age?
Another question is that of how other organs age. Where do carcinogens come from? Could the answer to this question lie in the strong carcinogens in fruits and vegetables that the plant kingdom uses to fight off other plants? Bruce Ames argues that these carcinogens are orders of magnitude more powerful than the environmental pollutants that concern us.
Bottom Line: We might want to think about what we can do to avoid premature aging of different various somatic tissues. The lives we save will be our own.