Colorectal cancer: symptoms, screening, stages and modern treatment

What colorectal cancer is

Colorectal cancer is a malignant tumour that starts in the lining of the colon or rectum. Almost all cases are adenocarcinomas. According to the World Health Organization it is the third most common cancer worldwide, with more than 1.9 million new cases and more than 900,000 deaths each year, and it is a leading cause of cancer death in Europe in both men and women.

Most bowel cancers develop slowly – often over ten years or more – from adenomatous polyps. These are benign growths in the bowel lining that, in some people, gradually accumulate genetic changes and become cancerous. This is why colonoscopy is so valuable: polyps can be found and removed before they ever turn into cancer.

Doctors distinguish between colon cancer and rectal cancer because treatment differs; radiotherapy and chemotherapy before surgery play a much larger role in rectal cancer.

Risk factors

Some risk factors cannot be changed, while others relate to lifestyle.

• Age – most cases occur after 50, although rates in people under 50 are rising in many countries.
• Family history – a parent, sibling or child with bowel cancer or advanced polyps.
• Inherited syndromes – Lynch syndrome and familial adenomatous polyposis, which cause cancer at a younger age and require earlier and more frequent surveillance.
• Long-standing inflammatory bowel disease – ulcerative colitis or Crohn's disease affecting the colon.
• Lifestyle – eating a lot of processed and red meat, a low-fibre diet, obesity, physical inactivity, smoking and alcohol.

Regular physical activity, a diet rich in vegetables, fruit and whole grains, limiting processed meat and alcohol, and not smoking all reduce risk. Read more in our guide to cancer prevention.

Bowel cancer symptoms

Early bowel cancer often causes no symptoms. When symptoms do occur, the most common are:

• blood in your stools – bright red or dark, mixed in with the stool;
• a lasting change in bowel habit – constipation, diarrhoea or alternating between the two for more than a few weeks, or narrower stools;
• a feeling of not emptying your bowel fully, or straining without result (especially with rectal cancer);
• abdominal pain, bloating or cramps;
• unexplained iron-deficiency anaemia – tiredness, pale skin, breathlessness on exertion; this is often the first and only sign of tumours in the right side of the colon;
• weight loss without trying;
• with an advanced tumour, signs of bowel obstruction (severe abdominal pain, vomiting, inability to pass wind or stools), which is an emergency.

Blood in the stools is most often caused by haemorrhoids or a small tear, but it should not automatically be put down to these, especially after the age of 40 to 50. A more serious cause should be ruled out first.

Screening: preventing bowel cancer

European guidelines recommend that men and women aged roughly 50 to 74 without symptoms take part in screening. The two main methods are:

Some countries start screening at 45. People with a family history, inherited syndromes or inflammatory bowel disease start earlier and are checked more often, following a personal plan from their doctor. In Bulgaria, a stool test for hidden blood can be arranged during the annual preventive check with your GP, and colonoscopy is available in gastroenterology departments. See also early detection of cancer.

Diagnosis and staging

The key test when bowel cancer is suspected is colonoscopy with biopsy. Once cancer is confirmed, staging usually includes:

• CT scan of the chest, abdomen and pelvis to look for spread to the liver, lungs or lymph nodes;
• pelvic MRI for rectal cancer, to assess local spread precisely (see MRI and CT scans);
• a blood test for the tumour marker CEA, mainly useful for follow-up (more in tumour markers);
• molecular testing of the tumour – microsatellite instability (MSI) or mismatch repair deficiency (dMMR), RAS and BRAF mutations and, in metastatic disease, HER2.

Treating colon cancer

The main treatment for localised colon cancer is surgery – removing the affected section of bowel with its lymph nodes and joining the ends. Many very early cancers and polyps with early malignant change can be removed endoscopically, without an operation. Much colorectal surgery is now done laparoscopically or with robotic surgery, which usually speeds up recovery, and enhanced recovery programmes (early mobilisation and eating) also shorten the hospital stay.

After surgery the pathologist confirms the stage. For stage III, and for some stage II cancers with high-risk features, adjuvant chemotherapy is usually recommended for three to six months to reduce the risk of recurrence.

For tumours with high microsatellite instability (MSI-H/dMMR), immunotherapy has proved highly effective in metastatic disease, and studies show striking results before surgery in locally advanced tumours.

Chemotherapy after surgery is usually well tolerated but can cause tiredness, nausea, diarrhoea and changes in blood counts. Oxaliplatin, which is commonly used, can cause tingling in the fingers and sensitivity to cold; in some people this lasts longer, so the doctor may shorten the course or reduce the dose. Recovery from surgery usually takes several weeks, and bowel habits may change for a while. Report any new symptoms to your team.

Treating rectal cancer and metastatic disease

Rectal cancer

For locally advanced rectal cancer, treatment often starts with radiotherapy or chemoradiotherapy, increasingly combined with chemotherapy before surgery (total neoadjuvant therapy). The aim is to shrink the tumour, reduce the risk of local recurrence and, where possible, preserve the anal sphincter. In some patients the tumour disappears completely, and in carefully selected cases at specialist centres a watch-and-wait approach may be discussed instead of surgery. A temporary or permanent stoma – an opening of the bowel onto the abdomen – is sometimes needed, and patients receive training and support.

Metastatic colorectal cancer

Even when the cancer has spread, many patients have real options for long-term control, and with limited metastases in the liver or lungs a cure is sometimes possible through surgery or ablation combined with chemotherapy. Systemic treatment is guided by the molecular profile:

• chemotherapy (combinations based on fluoropyrimidines, oxaliplatin and irinotecan);
• anti-EGFR antibodies – only for tumours without RAS mutations;
• anti-VEGF drugs that reduce the tumour's blood supply;
• targeted drugs for BRAF V600E mutations or HER2 amplification;
• immunotherapy for MSI-H/dMMR tumours.

This is why full molecular testing should be done at the start of treatment for metastatic disease. In some cases it can be performed using a liquid biopsy.

When to see a doctor, and follow-up

See your GP if you have:

• blood in your stools or black, tarry stools;
• a change in bowel habit lasting more than three to four weeks;
• abdominal pain or bloating without an obvious cause;
• unexplained weight loss, or tiredness with anaemia on a blood test;
• a family history of bowel cancer and you are 40 or over without having been screened.

Seek urgent help if you have severe abdominal pain with vomiting and cannot pass wind or stools, or if you have heavy bleeding.

After treatment, regular follow-up is usual: clinical reviews and CEA tests every three to six months, CT scans typically every six to twelve months in the first years, and a check colonoscopy after one year. Staying active and keeping a healthy weight after treatment are linked to better outcomes. For general principles, see our guide to cancer treatment.

Bowel cancer treatment abroad and in Türkiye

Patients from Bulgaria and across Europe often seek a second opinion, a fast colonoscopy or treatment at large accredited hospital groups in Istanbul, where colorectal surgeons experienced in laparoscopic and robotic surgery, modern radiotherapy and broad molecular testing are available. Check the surgeon's specialty (colorectal surgery), how many similar operations the team performs each year, whether cases are reviewed by a multidisciplinary tumour board, and that you receive a written plan that includes any chemotherapy after surgery. Agree, too, who will continue your treatment and follow-up at home. Organisers such as New City Clinic coordinate the hospital, doctor, hotel, transfers and interpreter; medical decisions remain with the doctors. If in doubt, ask for a second opinion.