Colorectal cancer occurs in the large intestine or rectum--the area where stool is stored until passed from the body. The American Cancer Society reports that nearly 147,000 people in the United States were diagnosed with colorectal cancer in 2009. Although disease rates have steadily declined since 1985, colorectal cancer remains the third most common cancer of Americans. Screening and vigilance for signs of colorectal cancer aid in early diagnosis and treatment.
Blood in the Stool
The Centers for Disease Control and Prevention warns that blood in the stool may be a sign of colorectal cancer. Bleeding elsewhere in the colon may not be visually noticeable. Doctors can check for unnoticeable blood with a stool occult blood test.
Constipation or Diarrhea
The onset of either diarrhea or constipation that lasts for two weeks or more may be a sign of colorectal cancer, notes the Mayo Clinic. Importantly, there may be alternation between constipation and diarrhea. According to "The Merck Manual for Healthcare Professionals," this alternation is suggestive of cancer in the colon on the left side of the body. Although these changes are not specific to colon and rectal cancer, they are important possible warning signs.
Decreased Stool Size
The University of Maryland Medical Center notes that a decrease in the diameter of the formed stool may be a sign of colorectal cancer. A tumor can impinge on the colon, causing a decrease in the open area for stool to pass through, leading to narrower stools.
Abdominal Pain and Bloating
The National Cancer Institute advises that abdominal pain, cramping and bloating may be signs of colon cancer. Left-sided colon cancer is particularly prone to causing abdominal cramping, although the correlation is not absolute. "The Merck Manual" notes that intense abdominal pain and tenderness may occur with colon obstruction, wherein the tumor prevents fecal material from moving through the large intestine.
Rectal Pain
Cancerous tumors of the rectum may cause rectal pain, advises "The Merck Manual." This symptom may be accompanied by an urgent need to move the bowels, even when little stool is present in the rectum.
Weight Loss and Fatigue
The University of California, San Francisco Medical Center points out that unintended weight loss and fatigue may be signs of colon or rectal cancer. Although they can be present with other types of cancer, these signs in combination with others that suggest a colorectal disorder can help guide diagnostic testing. Importantly, fatigue related to colorectal cancer may be augmented by tumor-associated blood loss leading to anemia.
