context: Your doctor will use tests to diagnose and learn the stage of your colon cancer. The stage tells whether it has spread and how far. Stage IV means your disease has traveled beyond your colon. You could have cancer cells in your liver, lungs, or other organs. Knowing where it has spread will help pinpoint the treatment that will work best for you. Let your doctor know if you have any of the following symptoms -- but keep in mind that many conditions can cause them. The sooner you get checked out, the better. Many people with colon cancer don't have symptoms. That's why it is so important to keep up with routine screening tests. When the disease -- at any stage -- causes symptoms, they may include: Blood (usually dark red or black) in the stool Constipation and diarrhea. These can also be symptoms of other, less serious conditions. But if they persist, see your doctor. Long, thin, pencil-like stools. These are a sign that something is blocking your colon. The blockage could be a tumor or something else. Fatigue and weakness. Feeling much more tired or weak than usual could be a sign that the tumor is bleeding and you've lost iron. Abdominal pain or bloating. Colon tumors can cause a blockage that makes it hard to fully empty your bowels. You can feel bloated and full as a result. Unexplained weight loss. A weight loss of 10 pounds or more, when you haven't changed your diet and exercise habits, could be cancer, especially if you also have other colon cancer symptoms. Nausea and vomiting, which may happen if the tumor causes an obstruction Other symptoms you have depend on where the cancer has spread. In the U. S., 20% of people who find out they have colon cancer learn that it has spread to distant parts of their body. Cancer can also spread "locally" through the lymph nodes and bloodstream. Colon cancer most often spreads to the liver, lungs, and peritoneum (the lining of the abdomen). This cancer can also reach the bones and other organs. Liver The liver removes toxic substances from the body and produces bile, a fluid used in digestion. Colon cancer can spread to the liver through a blood vessel that connects the intestines and liver. Many people don't have symptoms at first, if colon cancer is in their liver. If they do have symptoms, they may be vague and can include: Loss of appetite or feeling full early Fatigue Fever Itching Pain in the abdomen Swelling in the legs Weight loss Yellowing of the skin or whites of the eyes, called jaundice Lungs Because the lungs get blood flow from the rest of the body, cancer can travel there from other organs, including the colon. Cancer that has spread to the lungs often affects breathing. Symptoms include: A cough that doesn't go away Chest pain Blood in the mucus Trouble breathing Weight loss Peritoneum Cancer cells that break off from the main tumor can get into the lining of the abdomen. Symptoms include: Pain in the belly Loss of appetite Weight loss or gain Bones When colon cancer travels to the bones, it can weaken them and cause them to release stored calcium. Symptoms include: Bone pain Constipation, nausea, and loss of appetite from high calcium levels in the blood Broken bones Numbness or weakness in the legs and possibly the arms Pain in the back or neck Your doctor will first ask some general questions about your health. Then you will have one or more of these tests: Colonoscopy. You'll have this test in a hospital outpatient center, clinic, or at your doctor's office. With a tiny camera attached to a thin, flexible tube, your doctor will look for cancer inside your rectum and the entire large intestine. You'll have to prep the day before the test by drinking a liquid that cleans out your colon. Before the colonoscopy, you'll get medicine to make you sleep. The whole test takes about 30 minutes. Biopsy. During the colonoscopy or sigmoidoscopy, the doctor might remove a small piece of tissue. This is called a biopsy. Doctors will check it under a microscope to look for signs of cancer. Another way to do a biopsy is with a needle. A CT scan or ultrasound helps the doctor guide the needle to the tumor through your skin. Before a needle biopsy, you'll get a pain reliever at the site to numb the area. But you wouldn't get a needle biopsy for something inside your colon. Doctors do those biopsies for areas that are easier to reach, like the lung, liver, or peritoneum. These tests show whether the cancer has spread: Chest X-ray. An X-ray uses radiation in low doses to make images of structures inside your body. A chest X-ray can help your doctor see whether the cancer has spread to your lungs. CT (computed tomography). This powerful X-ray makes detailed pictures inside your body. The CT scan can show whether the cancer has spread to your lungs, liver, or other organs. Sometimes you'll get a special dye before the scan, either through a vein or as a pill. This dye gives a more detailed view of the cancer. MRI (magnetic resonance imaging). An MRI machine uses powerful magnets and radio waves to make pictures of organs and structures inside your body. This test can show where the cancer has spread inside your abdomen or pelvis. You may get dye before the test to create a clearer picture. Ultrasound. This test uses sound waves to make a picture of your organs. It can show whether the cancer has spread inside your pelvis or to your liver. Often during surgery to remove the tumor from your colon, the doctor will discover that your cancer has spread. The doctor might remove one or more lymph nodes during surgery and biopsy them to look for cancer. A pathologist will look at the tissue from your biopsy under a microscope and will write a pathology report that describes: The types of cells The size, shape, and other features of your cells, compared with cancer cells. ( This is called the grade.) How quickly the cells divide Whether the cancer has spread to other parts of your body Biopsy results can take 1 or 2 days, and sometimes longer. The pathologist might need extra time to get a second opinion. Or he may need to look at another tissue sample. Your doctor will stage your cancer based on your biopsy results. The stage tells: The size of your tumor Where it is Whether the cancer has spread Where it has spread Your doctor will use your tumor stage, test results, and other things to decide on the best treatment for your cancer. Ask questions throughout your diagnosis to make sure you understand your choices and your outlook.