Rectal cancer

What is it?

The rectum is the last part of the colon (the last fifteen 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 originates as a small benign polyp in the rectum that gradually becomes malignant over the years. When the tumour becomes malignant, it will gradually grow deeper into the wall of the rectum. In more advanced stages, the cancer even pierces the intestinal wall. 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. As a result, cancer cells 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 creates metastases, which, in the case of rectal cancer, are usually located in the liver and lungs.

Symptoms

• Blood loss during bowel movements.During early stages, microscopic amounts of blood can sometimes be found in the stools by means of stool tests.
• Change in bowel movement pattern(e.g. constipation, diarrhoea and anal mucus loss).

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. This provides essential information about the distance of the lesion from the anus and sphincter.
• Blood tests: besides the general information about the function of various organs, these provide an idea about 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 enables the identification and localisation of a tumour. Usually, tissue samples (biopsies) can also be collected for further microscopic examination. Microscopic examination of the biopsy can reveal whether the lesion is benign or malignant.
• CT scan: X-rays are used to visualise the chest and abdominal cavity. This will help determine whether the tumour in the rectum is also close to other organs. The presence of metastases in the liver or lungs can also be visualised with this examination.
• MRIor NMRscan: this magnetic scan shows the rectum in detail without using X-rays. This allows a better assessment of the depth of a lesion in the rectal wall. 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 rectal lesion is possibly a benign polyp, local resection (i.e. removal) can be considered. In this case, the tumour is removed through the anus with a narrow margin. For smaller lesions, this resection can be performed immediately during a colonoscopy.
• Larger lesions sometimes require surgical intervention through the anus. We call this a transanal endoscopic microsurgical resection or TEM. Microscopic examination of this extensive biopsy allows a definitive diagnosis to be made. If it proves to be a benign polyp, its total removal is usually sufficient. Further treatment with more extensive surgery, adjuvant radiotherapy or chemotherapy is then not required.
• If it is cancer, radiotherapy is sometime administered prior to surgery: 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: 15/05/2024