Maria, 52 years old, noticed that over the last two months her bowel function had changed. Sometimes constipation, sometimes the opposite, and one day she noticed a little blood on the toilet paper. She thought it was haemorrhoids and kept putting it off. She only saw a doctor when she started feeling fatigue that didn't go away with rest.

"The data and clinical case cited in this article are fictitious and are for purely illustrative purposes, serving to facilitate understanding of the topic addressed."

Stories like this happen quite often, because bowel cancer (also called colorectal cancer) usually gives signs well before being diagnosed. The problem is that many of these signs seem "too normal" to draw attention. According to the National Cancer Institute (INCA), this type of cancer is the third most frequent in Brazil, and the estimate is more than 53,000 new cases per year between 2026 and 2028. Understanding the warning signs is the first step to seeking help at the right time.

The first signs that appear in the bathroom

The bowel "tells stories" through what comes out of it, and it's there that the first warnings usually appear:

  • Blood in stools. It can be bright red blood or darker. Many people confuse it with haemorrhoids (and sometimes that's what it is), but bleeding that repeats itself deserves evaluation.
  • Change in the shape of stools. Thinner stools, in ribbon shape, in a persistent manner, may indicate a narrowing in the bowel.
  • Change in bowel habit. Constipation or diarrhoea that appear suddenly and continue for more than two or three weeks, especially if different from the pattern the person has always had.
  • Sensation that the bowel hasn't emptied completely, even after defecating.

One important point is worth noting: none of these signs, in isolation, means the person has cancer. Haemorrhoids, fissures, irritable bowel syndrome and diet also cause similar symptoms. What demands attention is persistence: symptoms that return, that have no clear explanation, or that last longer than a month.

The first signs that appear in daily life

Besides what happens in the bathroom, bowel cancer can also manifest itself more discreetly in routine:

  • Fatigue that doesn't improve with rest, often linked to anaemia (decrease in the number of red blood cells) caused by bleeding that the person didn't even notice.
  • Weight loss with no apparent reason, without changes in diet or exercise routine.
  • Recurrent abdominal pain or discomfort, like cramps, that comes and goes.
  • Sensation of bloating or persistent abdominal swelling.

These signs tend to be even more non-specific than those from the bathroom, and because of this they go unnoticed more easily. A recent survey by A.C. Camargo Cancer Center showed that, even among those who noticed blood in their stools, almost half did not see a doctor immediately. And an important fact: these signs deserve evaluation at any age, not just after 50 years old, since cases among younger people have been increasing.

How diagnosis works

The first step, even without symptoms, is screening, that is, looking for the disease before it gives signs. The entry-level examination is the faecal occult blood test (the SUS is incorporating the immunochemical version, more precise and without dietary restrictions, scheduled for the second half of 2026). This test identifies blood that is not visible to the naked eye.

If the result comes back altered, or if the person already has symptoms, the next examination is colonoscopy. In it, a thin tube with a camera travels through the entire large intestine, allowing direct visualisation of the intestinal wall, identification of polyps (lesions that can turn into cancer over time) and their removal at the same time, when possible. There are also other options, such as flexible sigmoidoscopy and CT colonography (the "virtual colonoscopy"), used in specific situations.

When there is confirmed suspicion, imaging tests (CT scan, MRI) and blood tests complement the investigation to understand the extent of the disease and plan treatment.

Who should start screening, and when

The Ministry of Health's recommendation for the SUS is to start screening at 50 years of age. Other guidelines, including international recommendations adopted since 2021, already indicate starting at 45 years of age, because of the increase in cases in younger people. Those with a family history of colorectal cancer or polyps, or inflammatory bowel diseases, usually need to start earlier, and this should be discussed individually with a doctor.

Risk factors

Some factors increase the chance of developing the disease:

  • Age above 45 to 50 years
  • Family history of colorectal cancer or intestinal polyps
  • Inflammatory bowel diseases, such as Crohn's disease and ulcerative colitis
  • Diet rich in ultra-processed foods, processed meats and deli meats
  • Sedentary lifestyle
  • Obesity
  • Smoking
  • Excessive alcohol consumption

Having one or more of these factors doesn't mean the person will develop cancer, but it helps the doctor determine whether screening should start earlier.

What can be done to reduce risk

The good news is that much of the risk can be addressed in daily life:

  • Prioritise fresh, unprocessed foods, with plenty of fibre (fruits, vegetables, legumes, whole grains)
  • Reduce consumption of ultra-processed foods and processed meats
  • Maintain regular physical activity
  • Avoid smoking
  • Moderate alcohol consumption
  • Keep weight within a healthy range
  • Don't put off screening, as it can detect and remove polyps before they turn into cancer

When to see a doctor

Bleeding in stools, persistent change in bowel habit, unexplained weight loss or unusual fatigue, for more than two or three weeks, are sufficient reason for an appointment. There's no need to wait for the symptom to "worsen" to seek help, and the sooner the investigation begins, the simpler the path to diagnosis and treatment tends to be.

This content is informative and educational in nature and does not replace medical consultation, diagnosis or treatment. Always seek a healthcare professional to evaluate your case individually.

Dr. Rebeca Soares Andrade CRM - GO 39335