It's best to get regular screenings rather than rely on colon cancer symptoms to alert you to the presence of a tumor. This is because colon cancer can grow for years before causing any symptoms. But, knowing what to look out for can't hurt.
Constipation Constipation, having a bowel movement less than three times a week, can be your body's way of suggesting that you make some minor adjustments in diet or exercise. However, constipation can also be a symptom of a colon cancer. In the beginning of the colon, waste material is slushy and can easily maneuver around anything that gets in its way. But as it nears the end of the colon, stool solidifies and is less forgiving of obstacles. A tumor in the rectum or far end of the colon can make it very difficult for waste to get by, thereby causing constipation.
Thin Stool Once stool is no longer in its slushy phase and begins to take shape, how it looks when it leaves your body can provide clues to what's going on inside. For example, thin stool can sometimes indicate that your waste squeezed by some sort of obstacle on its way out. In the case of colon or rectal cancer, that obstacle would be a tumor in the latter part of the colon or the rectum.
Stomach Cramps Sometimes a tumor causes a bowel obstruction, which is basically a road block in your colon. Depending on the severity of the blockage, solids, liquids, and even gas may be prevented from passing by. This leads to abdominal cramps that can be severe, especially if the blockage restricts blood flow to the colon. Painful cramps may also indicate that a tumor has perforated (poked through) the bowel wall; bowel perforation is a medical emergency.
Hematochezia (Bloody Stool) Tumors tend to bleed -- not a whole lot and not constantly, but they do bleed. As a result, some of that blood may show up in your stool. If the tumor is in the beginning of the colon, the blood will most likely be dry and virtually invisible by the time the waste leaves your body. However, if the tumor is in the rectum or toward the end of the colon, it may still be fresh and therefore, bright red.
Unexplained Weight Loss Many of us wouldn't want to question unexplained weight loss. We'd just be happy to be losing weight! But unfortunately, effortless weight loss is generally a sign that something is wrong. In the case of colon cancer, unexplained weight loss can be a sign that a tumor is releasing chemicals that are increasing your metabolism.
Sense of Fullness A tumor that grows toward the end of the colon or in the rectum may cause a sense of fullness. This is because your body senses that there's something else hanging around by its exit. What it doesn't know is that it's a tumor and it's attached, so it isn't going anywhere. It basically sees the tumor as a stubborn piece of waste, so you get that "I still have to go" sensation that can't be relieved.
Nausea and Vomiting Nausea and vomiting can occur for a lot of reasons. Motion sickness, an unpleasant sight or smell, a slew of common viruses, and drinking too much are all familiar causes. But sometimes, nausea and vomiting can be symptoms of something more serious, such as colon cancer.
Gas and Bloating A pattern of gas and bloating may be an indication that a tumor is growing in the colon and occasionally causing a blockage. Even if the tumor isn't large enough to cause a bowel obstruction on its own, stool may periodically get hung up on the tumor while it's passing by, causing a temporary obstruction. While your bowel is blocked and air is trapped, you'll be bloated. When the blockage resolves itself, all that air will need somewhere to go and you'll be gassy.
Lethargy Sometimes the presence of a tumor causes iron deficiency anemia, a condition that can cause you to feel extremely tired (lethargic). Tumors tend to bleed, which results in a loss of iron -- an element that transports oxygen to your cells. This symptom is characteristic of tumors in the beginning of the colon. Since it's pretty roomy there, tumors can get fairly big and bleed a lot before causing any other colon cancer symptoms. The blood usually dries before leaving the body, too, which also allows the bleeding to go unnoticed.
The Bottom Line Even though you have an idea of what to look out for, it's important to remember that a tumor can grow for years before causing any colon cancer symptoms. In addition, all of these symptoms are very poor predictors in and of themselves.
For most people, the best way to prevent colon cancer is to maintain a healthy lifestyle and receive regular screenings starting at age 50.
http://coloncancer.about.com/od/cancerprevention/a/Cancer_Symptoms.htm
Good luck and best wishes.