Colon cancer may cause no symptoms in its early stages. When symptoms do occur, new and persistent constipation or diarrhoea, a feeling that the bowel has not emptied completely, unexplained weight loss and weakness need attention. These symptoms also occur in other conditions, so cancer cannot be diagnosed from symptoms alone.
If a new change keeps recurring, affects your daily life or occurs alongside several other symptoms, do not delay seeing a doctor. Severe abdominal pain accompanied by vomiting, abdominal swelling and an inability to pass stool or wind requires urgent assessment. Do not wait for a scheduled appointment in this situation.
Why can the disease go unnoticed for a long time?
The large bowel is the part of the digestive system where stool forms. Its final section, the rectum, stores stool before it is passed. Cancer can develop when cells in the bowel lining multiply uncontrollably. In many cases, this process begins in a tissue growth called a polyp, but not every polyp becomes cancerous.
A small tumour may not obstruct the passage of stool, so a person can eat, go to work and continue daily life without any discomfort. Symptoms may appear as the tumour grows, affects bowel movement or causes small amounts of blood loss. There may be no visible change. Iron stores, however, gradually decline.
The absence of pain is not enough to be reassured. The reverse is also true: severe pain alone does not indicate the stage of the disease. There is no direct relationship between symptom severity and tumour spread that applies to everyone; the stage is determined by investigation results.
What changes might occur in everyday bowel habits?
The key comparison is with your own previous bowel pattern, not with other people. New constipation, more frequent bowel movements or alternating diarrhoea and constipation in someone who previously had a regular pattern should be investigated. A change lasting a day may be due to food, medication or infection, but symptoms that persist, recur and have no clear cause require more detailed investigation.
A feeling that the bowel is still full after going to the toilet.
Persistent or recurring abdominal cramps, bloating and discomfort.
A change in the appearance of stools together with a change in bowel habits.
Weight loss without dieting, reduced appetite and unexplained tiredness.
Unexplained iron deficiency and anaemia detected on blood tests.
In anaemia, haemoglobin, which carries oxygen in the blood, is reduced; tiring easily when climbing stairs, becoming breathless with less activity than before and pallor may be related to this change. Although iron supplements may improve some blood results, the reason for the low iron still needs to be investigated separately. New iron deficiency may indicate a need for digestive tract investigations, particularly in men and women who have been through the menopause.
Blood in the stool is also a warning sign and should be reported to a doctor. However, not seeing blood does not rule out the disease. Similarly, passing a narrow stool once is not a diagnosis; the doctor considers this change alongside its duration, accompanying symptoms and previous health.
Who is at higher risk?
Although the likelihood of colon cancer increases with age, it can also develop in younger people, so a new symptom should not be dismissed simply because someone is young. Having a risk factor does not mean the disease will definitely develop, just as having no known risk does not rule it out.
A history of colon or rectal cancer in a father, mother, sister, brother or child is important information for the doctor. The relative's age at diagnosis and the number of affected family members also matter. Information about certain types of polyps in close relatives should be shared too.
Some families have an inherited predisposition. For example, Lynch syndrome impairs the repair of errors in a cell's genetic material. Familial adenomatous polyposis is an inherited condition that causes numerous polyps to develop in the bowel. These conditions require specialist medical assessment, but a cancer diagnosis in one family member does not necessarily mean that other relatives have such an inherited syndrome.
A previous diagnosis of certain polyps or bowel cancer, as well as inflammatory conditions that affect the colon over a long period, increases risk. Ulcerative colitis and Crohn's disease affecting the colon are in this group. Irritable bowel syndrome is different. It is not itself considered a condition that increases colon cancer risk.
Smoking, excess weight, low physical activity, alcohol and a diet high in processed meat are also associated with risk. These factors are not listed to blame the patient. The disease can develop through a combination of causes and also occurs in people who lead healthy lives.
When should you not wait?
A persistent new change in bowel habits, unexplained weight loss, blood in the stool or unexplained anaemia is a reason to see a doctor soon. If you have a family risk, it is helpful to mention it at the start of the appointment. There is no need to set yourself a waiting period of several weeks, especially if things are getting worse.
Severe and increasing abdominal pain, repeated vomiting, marked abdominal swelling and an inability to pass wind or stool may suggest bowel obstruction. This means the contents of the bowel cannot move forward. A condition other than cancer may be the cause, but these symptoms still require emergency care, as do heavy bleeding, fainting, cold sweats and severe weakness.
What is assessed at the first appointment?
The doctor asks when the symptoms began, whether they are persistent, about weight changes, medicines and family history. After the examination, blood tests and bowel investigations suited to your needs may be planned. Taking a small sample of suspicious tissue and examining it under a microscope is called a biopsy; this investigation has a particular role in confirming a cancer diagnosis.
If cancer is confirmed, treatment is chosen according to the tumour's location and extent of spread. In suitable cases, laparoscopic surgery for bowel cancer, an operation through small abdominal incisions, may be part of treatment. Bringing previous blood test and examination results, together with a list of your medicines, reduces the need to gather the same information again.