What are symptoms of malignant neoplasms in the colon?

Symptoms of malignant neoplasms in the colon include red or very dark blood in the stool, a change in bowel habits, unexplained weight loss, frequent gas pains and stools that are unusually narrow, according to the National Cancer Institute. Other symptoms of the cancer include fatigue, vomiting and diarrhea.

In individuals with colon cancer, malignant cells form in the tissues of the colon, or large bowel of the digestive system, explains the National Cancer Institute. People at risk of developing the disease include those with a family history of colon cancer, ulcerative colitis or Crohn's disease or a personal history of certain other cancers or colon polyps.