Is the one just over-powering more common? If so, why? If the cancer comes from a genetic flaw in the individual, well, all the intestines (and everything else) has the same genetics. If the cause is basically exposure to some cancer-causing agent, wasn’t the small intestine already exposed to all the same things just a bit earlier than the colon?
Yes, colon CA is way more common. I’ve encountered occasional small bowel tumors in pathology practice, but the vast majority were of the less worrisome neuroendocrine type (a.k.a. “carcinoids”).
One key difference is that transit time through the small bowel is fast compared to the colon, so exposure to potential carcinogens occurs over a much longer period in the colon.
Note that for at least one kind of genetic susceptibility (Lynch syndrome), small intestinal carcinoma in those folks is about as common as colon cancer in the general population.
Different tissue has different genes expressed.
Huh. I would have guessed that stuff passed through one and the other at more or less the same rate. Wouldn’t you run into a growing (er) backlog otherwise?
Other thought: So, I’ve seen mention that it is ‘normal’ for people to crap anything between three times a week to three times a day. Does this affect their rates of getting colon cancer?
And idea for a new medical scam: induced diarrhea as a cancer preventative! Anyone want to invest in my new company?
As mentioned above, colon cancer is far more common
- The most common cancers (listed in descending order according to estimated new cases in 2020) are breast cancer, lung and bronchus cancer, prostate cancer, colon and rectum cancer, melanoma of the skin, bladder cancer, non-Hodgkin lymphoma, kidney and renal pelvis cancer, endometrial cancer, leukemia, pancreatic cancer, thyroid cancer, and liver cancer.
- Prostate, lung, and colorectal cancers account for an estimated 43% of all cancers diagnosed in men in 2020. For women, the three most common cancers are breast, lung, and colorectal, and they will account for an estimated 50% of all new cancer diagnoses in women in 2020.
I can’t get it to embed, but there’s a nice graphic at this link, showing the major cancers for men and women.
https://images.app.goo.gl/AmownqbR6s9v3KM17
There’s some evidence that chronic constipation is associated with a higher colon cancer risk.
“This study demonstrates an association, not causation, between chronic constipation and both colorectal cancer and benign neoplasms” said co-investigator Nicholas Talley, M.D., Ph.D., of the University of Newcastle. “The postulated causal link between constipation and increased colorectal cancer risk is that longer transit times increase the duration of contact between the colonic mucosa and concentrated carcinogens in the lumen, such as bile acids or other carcinogens.”"
There are other factors including genetic ones that are involved, and some disorders i.e. inflammatory bowel disease come with an increased risk of colon CA despite patients typically having a higher frequency of bowel movements.
Digested food mixed with water (Chyme) is liquid as it moves through the small intestine, which enables the the receptors on the villi that line the intestine to easily touch and absorb nutrients. Too much liquid, though, leads to diarrhea, so a major role of the large intestine is to absorb that water back into the system.
The elimination of the bulky water means that it all packs down into a smaller space. At the end, a solid, well-formed, but not overly hard stool should come out. If that’s not what you have life can be really uncomfortable. That’s why usually the first recommendation is to get more fiber in the diet (or by pills). Fiber absorbs water, so it can soften hard stools and harden liquid stools. (It also can be used as a floor polish.)
The small intestine is a very different environment from the large intestine. The colon is where the trillions of microorganisms - good and bad - live, manufacture gas and fatty acids, and also make up half the content of stools when they die. I’m not sure of a direct connection, but two different environments having two different rates of cancer isn’t going to surprise me.
Only if there was a constant influx. Instead you eat a lot of food at once, then it stays in the stomach for a while, then a short time in the small intestine before it slowly goes through your colon and … builds up a temporary backlog for you to deal with. Hopefully at a convenient time.
The whole process doesn’t have to complete before you eat again of course, but different time in different parts aren’t a mystery. 
Was your “floor polish” reference inspired by this? (audio only)
Yes, I am indeed that old to have seen it when new.
Sort of. Clearly at a global average rate stuff goes through at the rate you eat. Otherwise you’d inflate like Mister Creosote until you burst.
Your small intestine is ~20-25 feet long. Your large intestine is 2-3 feet long. Any given spot on the small intestine will be exposed to any given bunch of carcinogen ~10th as long as a spot on the large intestine.
Plus all the other differences explained by others above.
A guest lecturer from UK said he informally surveyed medical students at our school about what the size of the average adult bowel movement was. Answers ranged from 50grams to 3 pounds. Seems to go along with the idea that in some folks things sit in the large intestine longer than others.