The symptoms of colorectal cancer (cancer of the colon or rectum) are extremely variable, and depend on several factors, such as the cancer's site and size, and the presence or absence of bleeding or obstruction.
In most cases, polyps do not cause any symptoms. In a few cases (5%), polyps may cause bleeding, though this is usually only detectable by testing a specimen of the stool. In some cases, the patient may see bleeding that is visible to the naked eye, but a stool test will still be necessary to confirm this.
Colon cancer symptoms are easily confused with many other diseases of the stomach and intestine, and the early symptoms are often non-specific, such as tiredness or occasional loss of appetite. More worrying symptoms include anemia or weight loss, but the initial picture is often subtle, and may at first be ignored by the patient. Sometimes marked constipation will ring alarm bells, possibly alternating with diarrhea. The patient may also suffer from abdominal pains, which tends to lead the patient to the doctor sooner rather than later.
Colorectal cancer may be asymptomatic
The typical lack of distinctive symptoms often delays the diagnosis, reducing the chance of a good outcome. It is therefore very important to consult the doctor should any symptoms appear.
If a cancer grows really large, it may cause intestinal obstruction. This presents with intense abdominal pain, nausea, vomiting, failure to pass wind, and constipation. These symptoms are an emergency, and surgery is needed as quickly as possible.