DISCLAIMER
THE FOLLOWING INFORMATION IS NOT OFFICIAL MEDICAL INFORMATION AND SHOULD NOT REPLACE CONSULTATION WITH A MEDICAL DOCTOR ON COLON CANCER TREATMENT.

Read more on colon cancer symptoms at the American Society of Colon and Rectal Cancer web-site.

Based on wikipedia.com: 
Colon cancer early symptoms are usually unclear. They may include loss of weight, bleeding, and fatigue (feeling tired). Bowel (local) symptoms are not common until the tumor has developed to a large size. Usually, the closer the cancer is to the anus, the more noticeable the local symptoms will be. Bowel symptoms may include unexplained changes in habits of the bowel (or even a partial or total obstruction), abdominal pain, vomiting, and bloating. Furthermore, the doctor and/or the patient can feel a tumor in the abdomen. If the tumor had already invaded the bladder, it may cause pneumaturia (urine with air) and/or hematuria (urine with blood). If the cancer penetrated the vagina, it may cause redolent vaginal discharge. These are late events, indicative of a large tumor. Constitutional symptoms include unexplained loss of weight. However, weight loss may be a symptom of other cancers (e.g., esophageal). Additional constitutional symptoms may include anemia, causing dizziness, fatigue and palpitations. Metastases of the cancer in the liver may yield symptoms such as jaundice, abdominal pain, liver enlargement (usually felt by a doctor), and/or blood clots in the vessels (the blood becomes "thicker").

Read more about Colon Cancer treatment options.