Unfortunately, cancer is fairly common in dogs with an estimate of one in three dogs being affected. The risk increases as your dog gets older. But improved veterinary care means that dogs with cancer can now live longer and still enjoy a good quality of life. Early detection is vital - if you have concerns, take your dog along to the vet for a check-up before the disease reaches an advanced stage.

What is Cancer?

Cancer is the abnormal growth of cells. There are many different forms, depending on which tissue cells are affected. The causes of cancer, as in humans, aren’t completely understood. Toxins, radiation, viruses, problems with the immune system and genetic make-up are all possible causes.

Cancerous tumours that don’t spread are considered benign while cancers that spread to other parts of the body are known as metastatic or malignant. Malignant cancers are more aggressive and can spread through the body and affect organs including the brain, liver and lungs.

Signs and Symptoms of Cancer in Dogs

The signs of cancer in dogs can be very variable but weight loss, lack of appetite, depression, vomiting, diarrhoea, fever and being very tired are typical signs. Lumps and bumps or unusual skin lesions found on your dog may be harmless, but they can also be cancerous.

If you notice a new lump or an old lump has recently grown in size, ask your vet to check it out. The lump may be a lipoma (fatty lump), histiocytoma, cyst or wart but it could also be a mast cell tumour which can be serious. The survival rate depends on the type and the stage of the disease so never ignore any signs that all is not well with your dog.

Some types of cancer cause your dog more pain than others. Keep a look out for any signs such as limping, hunching, vocalising more than usual or any other unusual behaviour. They may also not want to be touched and may become aggressive.

Common Types of Cancers in Dogs

Like humans, there are many different types of cancer that affect different parts of the body. Some breeds of dog are more likely to be affected by a particular type. Cancer is the leading cause of death in some dog breeds such as the Boston Terrier, Golden Retriever, Great Dane, Rottweiler, German Shepherd, Boxer, Bulldog and Saint Bernard.

Common cancers found in dogs include:

Anal Sac Gland Sarcoma

This malignant tumour of the anal sacs is a relatively uncommon tumour in dogs. However, Cocker Spaniels seem to be particularly affected. In many cases, it only affects the anal sacs but, in some cases, it may spread to the lymph nodes or to the lungs, liver or spleen via the bloodstream. If the tumour is less than 3 cm in diameter, the tumour can be surgically removed. Radiotherapy may also be given. Large tumours may be treated by chemotherapy to shrink the tumour before surgery.

Brain Cancer

Brain tumours in dogs can cause a variety of signs - seizures (fits), blindness, changes in personality, lethargy, circling, and disorientation. As the tumour grows, it’ll cause pressure on the surrounding normal brain tissues. Brain tumours can also spread to other parts of the body. Treatment options include medication alone, medication and radiotherapy, or medication, radiotherapy and surgery. The aim of treatment is to allow your dog to have a good quality a life for as long as possible.

Haemangiosarcoma

This aggressive tumour affects the lining of blood cells causing a vascular mass to form. The skin, spleen, heart and other organs can be affected. While some skin forms are rarely metastatic, those affecting the spleen or heart are typically malignant. The tumour can grow and spread rapidly and can rupture causing profound blood loss. Treatment involves surgery, intensive care and chemotherapy for the best survival times. Haemangiosarcoma is often seen in middle-aged to older Golden Retrievers and German Shepherd dogs.

Lymphoma

Lymphoma in dogs is a cancer of the white blood cells. There are different forms - multicentric, thymic, alimentary, cutaneous, CNS, hepatic, renal and others. Swelling of the lymph nodes, lethargy, loss of appetite, difficulty breathing and vomiting may be seen. A biopsy of the tumour may be taken before the best treatment is decided. Most lymphomas respond well to chemotherapy. Treatment can provide some control over the condition and some dogs may be able to have several years of normal life following treatment.

Leukaemia

There are many forms of dog leukaemia – some may cause few problems for your dog while others can be fatal. In chronic leukaemia, there’s a slow and steady increase in white blood cells. In acute leukaemia, the white cell numbers increase rapidly, and the dog will become ill within days or weeks. Blood tests will show whether there’s an increase in white blood cells as well as a decrease in other types of blood cells. Bone marrow tissue examination and flow cytometry tests may also be carried out.

Mammary Gland Cancer

If your dog has a suspicious lump around the mammary area, it could be breast cancer. It’s common in older, female dogs that haven’t been spayed. Around half of all mammary tumours are malignant. If left untreated, the cancer can spread to other mammary glands, lymph nodes, lungs and other organs. Treatment involves surgery followed by radiation therapy or chemotherapy. Dogs that are spayed before their first heat cycle or before they’re a year old are less likely to develop breast cancer.

Mast Cell Tumour

Mast cell tumour (or mastocytoma) is a common type of skin cancer in dogs. As they don’t have a typical appearance, any lump or bump may potentially be a mast cell tumour. Boxers, Boston Terriers, and Golden Retrievers are most commonly affected. Tumours can be removed surgically, and this achieves a cure for most low-grade tumours. Higher grade tumours are more likely to spread. In addition to surgical removal, these may be treated with radiotherapy, chemotherapy and new therapeutic agents. 

Melanoma

The majority of skin melanomas in dogs are benign and are slow to grow, as are melanomas that affect the iris and the ciliary body of the eye. However, melanomas affecting the digits and oral cavity are malignant – they grow quickly and spread to other sites in the body. Breeds with heavily pigmented skin or oral mucosa (skin inside the mouth) are predisposed. Scottish terriers, Golden Retrievers, Poodles, and Dachshunds breeds are often affected. Treatment includes surgery along with chemotherapy, radiotherapy and/or immunotherapy.

Soft Tissue Sarcoma

Soft tissue sarcomas are tumours affecting the dog's connective tissue, muscle or nervous tissues. They’re usually painless and slow growing and appear as a firm mass on the skin. They generally occur in old dogs (8-9 years old) but, in Golden Retrievers, they can appear at a younger age. Mostly seen on the limbs, trunk and head, the tumours may be described as low, intermediate or high grade. A wide surgical margin is required to ensure a complete removal. Radiotherapy may also be necessary.

Osteosarcoma

This is a cancer of the bone and commonly affects large or giant breed dogs, e.g. Great Danes and Rottweilers. Tumours usually arise in the limbs but can also develop in the spine, ribcage or skull. Lameness may be seen and swelling in the bone at the cancer site may be hot and painful. Unfortunately, osteosarcoma can spread via the blood and secondary tumours may occur. Treatment may include amputation of the affected limb, chemotherapy and radiotherapy. As metastatic spread is common, the outlook is poor in the long term.

Transitional Cell Carcinoma

Transitional cell carcinoma (TCC) affects the dog's bladder. It’s a common cancer of the urinary tract in dogs. Breeds like the Scottish Terrier, Shetland Sheepdog, Beagle, Wire-haired Fox terrier and the West Highland White terrier are predisposed to TCC. Treatment includes surgery, radiation therapy, chemotherapy, stenting, and cystotomy. Prognosis is poor to fair, depending on the tumour stage. Early recurrence of the tumour, poor response to treatment, metastasis and difficulty in surgical removal of the tumour also affect the outcome.

How is Dog Cancer Diagnosed?

If you have any concerns, your vet will examine your dog and take x-rays, ultrasound scans, and blood and urine tests. To help diagnose cancer your vet may also take a sample of the tumour for examination under a microscope to check for cancerous cells and to determine which type of cancer your dog may have.

Samples can be taken by fine needle aspirate (a quick and simple procedure) or by biopsy where a small piece of the affected tissue is removed under anaesthesia for further examination. If lymphoma is suspected, a sample will be taken from the lymph node. To diagnose leukaemia, your vet may need to take a bone marrow sample.

MRI or CT scans may also be recommended, and your vet may refer your dog to a veterinary oncologist who specialises in treating canine cancers. Investigations can be expensive, but they’re the only way to determine exactly what type of cancer your cat may have.

How is Dog Cancer Treated?

Treating cancer for your dog will depend on the stage and the form of cancer they have been diagnosed with. In some cases, the treatment may bring about a complete cure but if the cancer has been discovered at an advanced stage, the treatment may be palliative.

This means that there’s no cure, but your vet will do all they can to enable your pet to live without pain and comfortably for as long as possible. Sadly, in some cases, there is nothing a vet can do and putting your pet to sleep may be the kindest option.

The treatment options are surgery, chemotherapy and radiotherapy (radiation therapy). Sometimes a combination of treatments is used. Solid tumours respond well to being surgically removed – especially those that haven’t spread, are relatively benign and easily accessible.

Chemotherapy is best for blood cancers or multiple tumours in the body while radiotherapy is often used when the size and extent of the tumour has been identified. Chemotherapy protocols for pets are designed to balance the beneficial effects against any potential side-effects. And don’t worry, hair loss is rare in dogs.

Your vet will go through the pros and cons of cancer treatment, so you make the best decision for your dog.

New cancer therapies have been developed recently with vaccines now available for canine osteosarcoma and melanoma. Your vet will discuss the best treatment for your dog with you so you can make the best possible decision for your furry friend.

If your dog is unwell and you suspect cancer, make an appointment as soon as possible with your vet. Depending on the type of cancer and how early it has been spotted, it may be treatable and carry a good chance of survival.

Early diagnosis and treatment can mean that your canine friend will be able enjoy a few more years with you. To help prevent your dog from developing cancer, keep your dog at a healthy weight, make sure they have regular exercise, provide a good diet and take them for regular veterinary check-ups.

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Content provided from Vetstream's Vetlexicon Canis - www.vetstream.com/treat/canis 

Vetlexicon is the world’s largest peer-reviewed online clinical reference source. All our content is written and peer-reviewed by over 1,000 of the world’s leading veterinarians, ensuring relevance, accuracy and quality.