Essential reminder before detailing these signs: colorectal cancer most often progresses silently for years. When symptoms appear, the disease is sometimes already at a more advanced stage. It is precisely for this reason that screening organized after the age of 50 remains more reliable than waiting for a symptom to appear.
1. Blood in the stools: the best known sign, but not always visible
It is the symptom most often associated with colorectal cancer in the public mind, and rightly so, it is a signal that should never be ignored. But it takes variable forms: bright red if it comes from the bottom of the rectum, darker or blackish if it comes from a higher part of the colon, sometimes completely invisible to the naked eye.
Rectal bleeding is not always of cancerous origin: hemorrhoids and anal fissures are very common benign causes. However, this never dispenses with medical advice, the only one capable of deciding between these different causes.
| Sign | Must alert if... | Common benign cause |
|---|---|---|
| Blood in stool | Bright red, black, or detected on toilet paper | Hemorrhoids, anal fissure |
| Transit modified | Changes permanently, lasts more than 2-3 weeks | Food, stress, passing virus |
| Finer stools | "Ribbon" appearance, unusual and repeated | Rare benign cause, to do check |
| Unexplained fatigue | Persists, associated with paleness or shortness of breath | Iron deficiency, other cause explore |
| Abdominal pain | New, recurring, lasting | Frequent functional digestive disorders |
2. Transit changes: duration matters more than intensityOccasional constipation or diarrhea, linked to a meal or a passing virus, is nothing to worry about. What should attract attention is a lasting and unusual change for the person: an alternation between diarrhea and constipation, a more frequent need to have a bowel movement, or a feeling of incomplete evacuation which persists beyond two to three weeks.
3. Lesser known signs: fatigue and thinner stools
Two signs are often underestimated because they do not seem directly related to the digestive tract. Unexplained and persistent fatigue can result from anemia caused by discreet and repeated digestive bleeding, invisible to the naked eye; a simple blood test can detect it. Abnormally thin stools, sometimes described as "ribbon-like", may reflect a narrowing of the intestinal diameter linked to a lesion which compresses the passage.
Unexplained weight loss, without a change in diet or physical activity, completes the list of general signs that should lead to consultation, particularly when associated with other digestive symptoms.
4. What generally should not worry
It is just as useful to know how to put things into perspective. Occasional bloating, long-standing and stable constipation, or menstrual pain in women are generally unrelated to colorectal cancer. The distinction is made on the new, persistent and progressive nature of a symptom, not on its occasional intensity.
⚠️ To remember from a medical point of view
Any new digestive symptom that persists beyond two to three weeks justifies a consultation, whatever the age, organized screening does not replace a consultation in the event of a symptom.
In menopausal women, rectal bleeding can sometimes be confused with gynecological bleeding: in case of doubt about the origin, a consultation makes it possible to clarify the situation.
Consult urgently in case of severe abdominal pain, repeated vomiting, complete cessation of stools and gas, or heavy digestive bleeding.
