How does bowel cancer damage the digestive system?

Obstruction: The main function of the large intestine is to absorb water to convert the liquid digestive by-products into a solid form. This physiologic function is essentially unaffected by a cancer. However, as the cancer grows, it may obstruct the intestine, leading to pain, bloating, and (rarely) rupture. Furthermore, these tumors often bleed, leading to anemia, which can make one feel tired and weak.

Need more info: In order to be able to comment on prognosis, it's important to have some more information. What type of cancer (adenocarcinoma versus neuroendocrine)? Where within the small bowel is it located? Has it spread to other organs? Can it be removed completely with an operation? Small tumors that have not spread often have a good prognosis, but talk to your doctor to find out about your case.