If cancer (mostly) results from the degradation of DNA, then it would be logical to think that one’s chances of getting cancer increase as one ages. Is this the case? In historical times (when the average life span was less than 40 years), was cancer a rare disease?
I believe that yes, the likelihood of getting some kind of cancer increases as you age. If you are interested in the history of cancer, I highly recommend The Emperor of All Maladies: A Biography of Cancer by Siddhartha Mukherjee. The audio version is read by the author, and is a great listen.
More specifically than just general degradation of DNA, cancer arises when the programming that controls and restricts cell proliferation to coordinate body development is compromised. Since there are numerous checks and balances, and several DNA repair mechanisms, mutations have to accumulate in numerous key genes (but not always the same ones) before cancer arises. This is a random process, the more time available, the more chance there is that a mutation hits something that matters. This is also why a specific case of cancer cannot usually be assigned to a single cause; we think in terms of risk factors. Everything environmental that “causes cancer” is, in one way or another, increasing the mutation rate, and thereby increasing the risk that a random mutation hits something that matters.
Yes, cancer is mostly (but obviously not exclusively) a disease of aging. A previous thread covering some of the issues.
I recently read somewhere (probably last Tuesday’s Science Times) that while cancer is the second leading cause of death in developed countries (after heart diseases) it is well down in the third world. Of course, some younger people are afflicted, but it is relatively rare.
Obviously there are more things that are going to kill you in countries where infectious disease is still big. But cancer is a huge issue in the developing world, especially as there is little recognition of the problem and few resources addressing it. Things like wood cookstoves, aflatoxin (a carcinogenic mold that grows on improperly stored grain), untreated STDs, and environmental pollution all contribute to the cancer rate.
“we know that cancer is mainly a disease of the elderly – three quarters of cases diagnosed in people aged 60 and over, and more than a third (36 per cent) of cases in people aged 75 and over. So it’s not surprising that cancer was a rare event in populations where people were unlikely to make it past 40.”
I think if you plot a graph of cancer incidence by age you get two peaks: one in infancy and a (much larger) ramp with increasing age.
IIRC, infancy is a higher risk period than, say, adolescence because there is so much stem cell activity and cancers directly or indirectly caused by genetics may manifest immediately.