Bowel Cancer

Bowel cancer in dogs – this sounds alarming at first, but fortunately it is rare: Only about 1–2% of all dogs are affected, and most do not fall ill until their eighth year. Medically, it is a malignant tumour in the small or large intestine that unfortunately often develops silently.

That is exactly what makes it insidious. The condition causes no problems for a long time – until the tumour is large enough to block the bowel or cause bleeding that darkens the faeces. Until then, you often suspect nothing.

What types of bowel cancer are there in dogs?

Adenocarcinoma is the most common form – it accounts for around 60% of all bowel tumours. It arises in the mucosal cells and grows aggressively into the bowel wall, usually in the large intestine.

Lymphomas originate from degenerated immune cells and more often affect the small intestine. With about 25% of cases, they are the second most common group – and they often respond better to chemotherapy than adenocarcinomas.

Leiomyosarcomas are rarer. They grow from the muscle layer of the bowel wall and can become surprisingly large before causing any symptoms at all. A particular danger: these tumours can rupture into the abdominal cavity.

How do I recognise bowel cancer in my dog?

Blood in the faeces is often the first sign – however, not fresh red blood like from a scrape, but rather dark streaks or a black discolouration. This indicates a bleeding source further up in the bowel.

Changes in defecation habits develop gradually. More frequent passing of small amounts, constant switching between constipation and soft faeces, sometimes slimy faeces or a changed odour – all of this can be an indication.

Weight loss despite normal appetite is also suspicious. A tumour can damage the bowel surface so much that proteins and fats are simply no longer absorbed – the dog eats, but the body still does not get the nutrients.

Vomiting that occurs repeatedly over several days – often after eating – is another signal. This is different from a short-lived upset stomach; here the tumour causes a backup of bowel contents.

Abdominal pain manifests differently: cramped posture, whining when the abdomen is touched, sudden standing up from lying down, or a noticeably arched back. Many owners first notice only that ‘something is not right’.

How is bowel cancer in dogs diagnosed?

Initial clues can already be provided by palpation. An experienced vet feels thickenings or painful areas in the abdomen – larger tumours can already be felt this way.

X-rays show bowel narrowing or blockages. Contrast medium is often used so that the course of the bowel becomes visible. You should plan for about two hours for the entire examination.

Ultrasound can display tumours from around one centimetre in size – and simultaneously shows whether the cancer has already spread to lymph nodes or other organs.

The most precise method is endoscopy: a direct view into the bowel, combined with a tissue sample. The dog receives a short anaesthetic for this. The result of the tissue examination is usually available after two to three days.

What treatment options are available?

Surgery is currently the only treatment that actually aims for a cure. The surgeon removes the affected section of bowel and sutures the healthy ends together. This is fully successful in about 40% of cases.

If surgery is fully successful, affected dogs live on average another 18 to 24 months without symptoms. With incomplete removal, this period shortens to six to eight months – a big difference that shows how important early detection is.

Chemotherapy is used primarily for lymphomas. About 60% of dogs respond to it and show at least temporary tumour shrinkage. Treatment usually takes place every three weeks, over four to six months.

If a cure is no longer possible, pain management and dietary adjustments take centre stage. Easily digestible food in smaller portions relieves some of the daily burden on the diseased intestine.

Are there preventive measures?

Unfortunately, there is no targeted prevention against bowel cancer. However, what can help: from the seventh year of life onwards, have the faeces regularly tested for occult – i.e. invisible – blood. This allows early signs to be discovered before they are visible to the naked eye.

Boxers, German Shepherds and Golden Retrievers are affected disproportionately often. If you have one of these dogs, you should not wait until the seventh year – from the fifth year of life onwards, an annual thorough examination is advisable.