Diarrhea
The opposite of constipation, diarrhea is also frequent in colon cancer. Many patients would experience an alternation between constipation and diarrhea, especially after they start their cancer meds. In some cases, watery diarrhea associated with colon cancer might be severe enough to cause dehydration and electrolyte problems, especially in the elderly. Many reasons would cause an alternation between constipation and diarrhea, such as inflammatory bowel disease, which should be ruled out before suspecting colon cancer.