How does rectal cancer affect the body?

Depends on staging: Rectal cancer can cause problems with the rectal function, based on it's presence or from treatment related side effects, such as rectal bleeding. More serious problems including weight loss and fatigue may occur if the cancer has spread.

Depends: Early on there may be no effect. As the disease progresses undiagnosed, you may develop a change in bowels, blood in stool, abdominal pain, weight loss, loss of appetite, lethargy, loss of stamina, bowel obstruction, shortness of breath, anemia, early diagnosis in high risk patients or regular colonoscopies is the best way to avoid all of the above.