Rectal cancer

What is it?

The rectum is the last part of the colon (the last 15 centimetres measured from the anus). Thanks to its larger diameter, the rectum acts as a reservoir for the bowel movement before it leaves the body as stool. At the level of the anus, there is the sphincter muscle which is necessary to control the stool (the continence).

Rectal cancer develops as a small benign polyp in the rectum that gradually becomes malignant over the years. When the tumour has become malignant, it will gradually grow deeper and deeper into the wall of the rectum. In more advanced stages, the cancer even pierces the intestinal wall and the malignant tumour can grow into neighbouring structures such as the bladder, prostate, vagina, sacrum or sphincter. As the tumour grows deeper, it can also affect the wall of smaller blood vessels and this way, enter the bloodstream. A malignant tumour also tends to spread via the lymphatic pathways, causing the cancer cells to end up in the adjacent lymph nodes. These glands initially act as protective filters, but as they are affected by the tumour, malignant cells can also enter the bloodstream via this route. When cancer cells arrive in the bloodstream (either through the lymphatic pathways or through direct growth in the blood vessels), they can spread in the body and implant in other organs. This allows for spreading or metastases, which, in the case of rectal cancer, usually take place in the liver and lungs.

Symptoms

The lesions are normally found due to blood loss during bowel movements or a change in the bowel pattern (constipation, diarrhoea, anal loss of mucus...). During early stages, microscopic amounts of blood can sometimes be found in the stools by means of stool tests.

Diagnosis

To make a diagnosis and assess the seriousness of the situation, a number of additional examinations are required:

• Physical examination: in addition to a general examination of the abdomen, your physician will usually also carry out an internal examination of the anus with the finger. During this examination, the tumour can sometimes be felt, which provides essential information about the distance of the lesion from the anus and sphincter.
• Blood test: besides the general information about the function of different organs, these provide an idea of the extent of a specific tumour marker: the Carcinogenic Embryonic Antigen (or CEA). This protein usually builds up when a colon or rectal cancer spreads or re-emerges at a later stage. It is therefore a sensitive parameter to continue monitoring patients who have bowel cancer during the months and years following surgery.
• Endoscopy: during a colonoscopy or intestinal examination, an internal examination of the colon is performed with a flexible camera. This will allow to identify and localise a tumour and take tissue samples (biopsies) for further microscopic examination. Microscopic examination of this biopsy may reveal whether the lesion is benign or malignant.
• CT scan: X-rays are used to visualise the chest and abdominal cavity. This scan allows practitioners to determine whether the tumour in the rectum is also in the vicinity of other organs. The presence of metastases in the liver or lungs can also be visualised with this examination.
• MRI or NMR scan: this magnetic scan shows the rectum in detail without using X-rays. This allows to estimate the depth of a lesion in the rectal wall better. The presence of suspicious lymph nodes near the rectum can usually be better assessed with an MRI.
• Endoscopic ultrasound (EUS): an anal ultrasound device can sometimes be used to assess the depth of limited lesions. For more advanced malignant tumours, an NMR is usually sufficient.

Treatment

• If the lesion in the rectum is still a benign polyp, a local resection (i.e. a removal) can be opted for. In this case, the lump – including a limited margin – is removed through the anus. In case of smaller lesions, resection can be done immediately during the colonoscopy.
• Larger injuries sometimes require surgical intervention through the anus, which we call transanal endoscopic microsurgical resection or TEM. Based on microscopic examination of this large biopsy, a definitive diagnosis can be reached. If it proves to be a benign polyp, its total removal is usually sufficient and further treatment, such as more far-reaching surgery, radiation or chemotherapy, is not necessary.
• If it is cancer, radiotherapy is sometimes given prior to surgery. Read more here about radiotherapy for rectal cancer.
• The removal of the tumour with a safe margin can also be done by surgical removal of the rectum.

Latest publication date: 19/01/2024