What are the causes of colon cancer?

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.

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.

Colon cancer: Nobody know for sure. However, recent studies showed genetic mutations in tumor suppressor gene such as apc can be detected in majority of sporadic colon cancer, while dna repair gene mutation account for some high risk colon cancer syndromes known as lynch syndrome. The risk factors include die (fat), alcohol/smoking, prior polyps, ibd, and family history, etc.

Very complicated: Monoclonal theory says that just like we are a living thing, we are born, we have jobs to do and then we die, each cell has a similar cycle of birth, life, and death. Cancer occurs when a cell develops so many mutations that it does not follow that cycle and does not die but can still divide itself and hides from our immune system which is there to detect abnormal cells and destroy them.