when I started medical school, most colon cancer was in the rectum, so we had to do rectal examinations on all our patients, since over half the cancers were withing finger lengthe of the anus. We family docs also learned how to do simple sigmoidoscopies, using the hard tube type (later, the flexible one was used, but by that time, we had enough specialists so I stopped doing them).
To cure them, they removed the rectum and diverted the colon to drain into a colostomy bag...and we had lots of discussions if they could later join or divert the feces to the anus, which had a sphincter, for social reasons.
But as time went on, these cancers became more rare (I hadn't seen one in the last 10 yrs of medicine). But colon cancer upstream increase so the emphasis was to do colonoscopies.
This is a more invasive procedure, often requiring some anesthesia, and an expensive scope and lots of training to do it well.
So how should we screen? Well, if you do "occult blood" screenings, often folks never bring them back, and there is a high false positive and false negative rate.
We did see colon cancer in young people: we had a family where one aunt died at age 34, and although funds for the IHS were limited, we tried to get the family screened...we even had a 7 year old sent out for a pediatric colonoscopy at a specialized center (she had pre cancerous polyps removed)...
So why are there more colon cancer? Or is it just that older folks are picked up and their pre cancerous polyps removed before they turn into cancer?
And is the changing history due to diet? Burkett noted that colon cancer was rare in east Africa, where high fiber corn sadza was the main food. So yes, fiber probably helps, by increasing transit time i.e. getting rid of toxins (yes, this sounds like those colon cleansing fads, but there is a small bit of truth in them: They merely exaggerate to make money).
Meat may increase the rate, or maybe it just means if you eat meat, you get less fiber in your diet.
Ironically, aspirin and Ibuprofen cut the rate of colon cancer.
In the meanwhile, stomach cancer, which was almost an epidemic at the turn of the 20th century, pretty well disappeared as smoked food was replaced with chemicals to keep them from rotting.
Nowadays, if you get a stomach cancer, it is probably lymphoma (something almost unheard of when I was in medical school...and again, I have had two patients with stomach lymphoma in my last ten years of practice but no cancer of the stomach for the last 20 years of practice)
something I will have to search google about.