Understanding colorectal cancer

Most people's minds go blank when they first hear this diagnosis. This article has a simple purpose: to help you understand a few basic things, so that you can ask useful questions when you next speak to your doctor.

What the large bowel does

After the stomach and small intestine have digested and absorbed food, what remains passes into the large bowel. Its main job is to absorb water, gradually turning liquid contents into formed stool.

The large bowel is about a metre and a half long: the caecum, ascending colon, transverse colon, descending colon, sigmoid colon, and finally the rectum and anus. A tumour in a different position causes different symptoms and is treated differently, which is why your doctor pays so much attention to exactly where it is.

How the cancer develops

Most colorectal cancers begin as a small benign polyp and change slowly over several years. Because the process is slow, there is an opportunity to remove it at colonoscopy while it is still a polyp.

Why polyps form relates to age, diet, obesity, smoking, alcohol and lack of exercise, and partly to inheritance. For most patients no single cause can be identified. Please do not spend your energy blaming yourself.

Common symptoms

• A change in bowel habit: constipation, diarrhoea, or alternating between the two.
• Blood in the stool, or darker stool.
• Stools becoming narrower.
• Abdominal pain or bloating.
• Unexplained weight loss.
• Tiredness and pallor caused by anaemia.

One thing to keep in mind: early disease often causes no symptoms at all. By the time symptoms are obvious, the stage is often later. That is the reason screening exists.

Which tests are done

Diagnosis usually needs several tests, each with its own job:

• Colonoscopy — sees the tumour directly and takes a tissue sample. This is how the diagnosis is confirmed.
• Imaging — CT or MRI, to judge how far the tumour has grown and whether it has spread to other organs. Rectal cancer usually needs more detailed imaging.
• Blood tests — including tumour markers, mainly as a reference point before and after treatment.

What the stage means

Your doctor judges the stage from three things: how deeply the tumour has grown into the bowel wall, whether nearby lymph nodes are involved, and whether it has spread to other organs.

The stage shapes the treatment plan, but it is where treatment starts, not how it ends. Two patients at the same stage can have very different outcomes, depending on the tumour's characteristics and how it responds. Put your attention on what happens next, rather than searching online for survival figures — those come from data gathered years ago, and they were not calculated for you.

How it is treated

• Surgery — the main treatment for most patients. Besides open surgery, there are minimally invasive approaches including laparoscopic and da Vinci robotic surgery. Which one is used depends on the tumour's position and extent and on your general health.
• Chemotherapy — medicines that act on cancer cells that may already have spread but cannot yet be seen on scans. Some people have it after surgery, some before.
• Radiotherapy — used mainly for rectal cancer, often together with chemotherapy, to shrink the tumour, make a complete resection more likely, and reduce local recurrence.
• Targeted therapy and immunotherapy — suitability depends on the tumour's genetic and molecular tests. This is why pathology and gene reports are awaited after surgery.

Three questions people often ask

"Will I need a stoma?" Not necessarily. It depends on where the tumour is and whether the anal sphincter can be preserved. There is also a difference between a temporary and a permanent stoma; a temporary one can usually be closed after a few months. Ask your own surgeon which applies to you.

"Will my children inherit it?" Usually not. But if you developed it at a younger age, or several people in the family have had it, your doctor may suggest further testing and arrange screening for relatives.

"Can I live normally during treatment?" Most people can. Work, eating and exercise can largely continue, with some adjustment of pace. The specific limits depend on the treatment you are having.