Combination . Environmental and genetic factors can increase the likelihood of developing colorectal cancer. 70% of cases are sporadic cases, only about 10% is a true inherited cancer and approximately 25% is familial type. Some risk factors include- inflammatory bowel disease, dietary habit ( processed red meat), dm, alcohol, growth hormone, obesity, cigarette, immunosupressant , age, etc.
Depends. 20% are genetically caused, the remainder being environmentally caused by some as yet unknown combination of exposures to various agents. The person who finds the actual answer will no doubt be on a south pacific island relaxing after having won the nobel prize. We just don't know in every case.
Rectal bleeding is c. Colon cancer can be entirely silent disease, producing little or no symptoms when early and localized to the bowel. So screening with colonoscopy in asymptomatic subjects is advised to look for polyps which are precursors of colon cancer. Rectal bleeding and abdominal pain can be symptoms of this cancer but they are often not early symptoms. The cause of colon cancer is not known. Read more...