The most common symptoms of rectal cancer are blood in the stool, a change in bowel habits that does not go away, the feeling of not having emptied completely after a bowel movement (tenesmus), stools that are narrower than usual and mucus. In the early stages it may cause no symptoms at all, and many of these symptoms also appear in benign conditions such as hemorrhoids. That is why a symptom that persists or keeps coming back needs to be investigated.
Why does rectal cancer cause different symptoms from colon cancer?
The rectum is the last section of the large bowel, just before the anus. A tumor there is very close to the exit, so the blood is usually visible and changes in bowel movements are noticed earlier. In the right colon, by contrast, bleeding is usually hidden and sometimes the first sign is anemia with no other explanation.
This does not mean rectal cancer always gives a warning. In its early stages it often causes no symptoms, which is why some cases are found through screening tests before the patient notices anything.
What are the symptoms of rectal cancer?
The most common are blood in the stool, a change in bowel habits that does not go away and the feeling of not having emptied completely. None of them is specific to cancer, but when they persist they need to be investigated.
- Blood in the stool. It can be bright red, mixed in with the stool or darker. It may also be invisible and only show up in a fecal occult blood test. What each color means is covered in blood in stool.
- A change in bowel habits. Diarrhea or constipation in someone whose bowels used to be normal, or periods of one and then the other.
- Tenesmus. A frequent urge to go to the toilet even though little comes out, with the feeling that something is still there.
- Narrower stools than usual, ribbon-like or pencil-thin, over a sustained period.
- Mucus in the stool.
- Discomfort or pain in the rectal or anal area, especially during a bowel movement. It tends to appear later than bleeding.
As the disease progresses, tiredness from anemia (slow blood loss over weeks or months), unexplained weight loss and loss of appetite may follow.
When should I go to the emergency room?
If you have severe abdominal pain and cannot pass stool or wind, or if you are bleeding heavily. In advanced stages the tumor can block the passage of stool, and the signs are:
- Severe, cramping abdominal pain.
- A swollen, distended abdomen.
- Difficulty or inability to pass stool and wind.
This is a bowel obstruction and needs urgent assessment. Depending on the case, emergency surgery may be needed or, in selected situations, a stent can be placed to unblock the bowel so that surgery can be done later in better conditions. Heavy bleeding is also a reason to go to the emergency room.
Is it hemorrhoids or could it be cancer?
This is the most common question, and looking at the blood will not answer it. Hemorrhoids and anal fissures are far more common than cancer and also cause bright red bleeding. But the two can occur together, and if the bleeding is put down to hemorrhoids without an examination, a cancer can go undiagnosed for months.
Some signs point more towards something that needs a full work-up:
- The blood is mixed in with the stool, not just on the paper or the surface.
- The bleeding comes with a sustained change in bowel habits, tenesmus or narrower stools.
- There is tiredness, anemia or weight loss.
- Close relatives have had colorectal cancer or polyps.
- The hemorrhoids have already been treated and the bleeding continues.
None of these signs confirms or rules anything out on its own. What settles the question is an examination by a specialist and, if needed, a colonoscopy.
Can younger people get rectal cancer?
Yes, and increasingly so. More and more colorectal cancers are being diagnosed in people under 50, and at that age the rectum is a common site. Because younger people are not included in screening programs and their symptoms tend to be blamed on hemorrhoids or a minor digestive problem, the diagnosis often comes later. Being under 50 is not a reason to leave recurring bleeding uninvestigated.
When should I see a specialist?
It is worth asking for an assessment if any of these symptoms lasts more than two or three weeks, keeps coming back or has no clear cause. Most of the time they are due to benign problems, but they need to be investigated to rule out cancer. If you have a family history of colorectal cancer, see a doctor even if the symptoms are mild.
How is the diagnosis confirmed?
With a colonoscopy and a biopsy of the tumor, followed by a pelvic MRI that shows how far it has spread. The full work-up is usually done in these steps:
- Examination and digital rectal exam in clinic. It allows the doctor to feel lesions in the lower rectum and narrow down the cause of the bleeding.
- Full colonoscopy with biopsies. It confirms the diagnosis, and in rectal cancer we always ask for a complete one to rule out other lesions in the rest of the colon. If it cannot be completed, a CT colonography (virtual colonoscopy) is used.
- Pelvic MRI. For the rectum this is the key test to see how far the tumor has grown, how far it is from the anus and whether nearby lymph nodes are involved. The treatment plan depends to a large extent on it.
- CT scan of the chest and abdomen to check for spread to the liver or lungs.
- Blood tests with tumor markers such as CEA, which are later useful for follow-up.
What happens after the diagnosis?
Treatment is planned, and it often combines several phases. At Memorial Publio Cordón Hospital every case is reviewed by a team of surgeons, oncologists, radiologists and gastroenterologists before anything is decided. The usual approach is radiotherapy and chemotherapy before surgery to shrink the tumor, followed by an operation adapted to its location. Whenever possible the aim is to preserve the sphincter and avoid a permanent stoma. Robotic surgery adds precision in the pelvis, a narrow space surrounded by nerves that matter for urinary and sexual function.
In selected cases where the tumor disappears completely after chemotherapy and radiotherapy, surgery can sometimes be avoided with very close follow-up. We explain this in watch and wait in rectal cancer.
The earlier the disease is found, the better the chances of cure and the more options there are to preserve the rectum. If you already have a diagnosis and want to check the proposed plan, you can ask for a second opinion.
Frequently asked questions
What is the first symptom of rectal cancer?
The most common is blood in the stool, often red and visible. But in the early stages there may be no symptoms at all, which is why some cases are found through screening tests.
Does rectal cancer hurt?
At first it often does not hurt. When there is pain, it is felt in the rectal or anal area, especially during a bowel movement, or as a feeling of not having emptied completely. It usually appears later than bleeding.
How can I tell whether bleeding is from hemorrhoids or cancer?
You cannot tell for sure from how the blood looks. Hemorrhoids are much more common, but both can happen at the same time. If the bleeding keeps coming back, is mixed in with the stool or comes with changes in bowel habits, it needs to be examined and, if the specialist recommends it, a colonoscopy done.
What do stools look like with rectal cancer?
They may contain blood or mucus and be narrower than usual over a sustained period. There may also be new diarrhea or constipation. No particular appearance confirms cancer: what matters is that the change persists.
Can a young person get rectal cancer?
Yes. It is more common from the age of 50, but it is increasingly diagnosed in younger people. Age is not a reason to leave recurring bleeding uninvestigated.
How long should I wait before seeing a doctor?
If a symptom lasts more than two or three weeks, keeps coming back or has no clear cause, see a doctor. With severe abdominal pain and inability to pass stool and wind, or with heavy bleeding, go to the emergency room.
References
- US National Cancer Institute. Rectal Cancer Treatment (PDQ®), Patient Version.
- National Institute for Health and Care Excellence. Suspected cancer: recognition and referral (NG12).
This information is for general guidance and does not replace an assessment by your doctor.