With veterinary healthcare advancing and positively impacting the quality of life of companion animals, here’s unpacking some tenets about cancer in animals!
National Cancer Awareness Day in India is observed on the 7th of November each year to educate people and make them aware of cancer, its symptoms, and its treatment. According to the WHO, cancer is the second leading cause of death in people every year. While such data is not available for animals, as veterinary healthcare makes strides every single day and the quality of life of companion animals continues to get extended, health issues that impact their quality of life such as this dreaded disease are also on the rise. So, let’s try to unpack some tenets about this condition.
What Is the Basic Definition of Cancer?
It is a broad term to denote abnormal and uncontrolled cell growth with the potential to invade other cells or spread to other parts of the body.
Cancer falls into a subset of neoplasm, which is basically a group of cells that have undergone unregulated cell growth, forming lumps or masses.
There are two types of growths: Benign and Malignant. Benign tumours are not considered cancerous. They are usually encapsulated in a well-defined capsule and do not spread to other areas or invade other cells or organs. The pressure exerted by such growths on blood vessels or nerves may be dangerous, but usually, they do not pose a risk to the quality of an animal’s life. Malignant tumours, on the other hand, are not restrained or encapsulated. They spread and invade other cells and organs by a process known as metastasis. Malignant tumours need a rich blood supply to spread to other parts of the body and will often take up essential blood supply, which is needed by the animal or organism, eventually leading to death.
What Are the Common Types of Cancer in Dogs?
This kind of cancer affects the scent glands that are located on either side of a dog’s anus. It is equally common in both male and female dogs, usually over the age of 10 years. Anal gland cancer is highly metastatic and fatal.
- Bladder cancer aka Transitional Cell Carcinoma:
It is so-called because it is the cancer of the deeper layer of muscles of the bladder wall. As the tumour grows, it may block the urethra; obstructing urine flow or stopping it entirely. This kind of cancer is more commonly observed in middle-aged females.
Cancer which develops from the blood vessels, leading to the formation of tumours on the spleen, skin, liver and heart. This can affect any breed or gender of dogs but is commonly seen in middle to older age dogs.
This is a silent and deadly killer, which is often a large singular tumour called hepatocellular carcinoma. It doesn’t often show any significant clinical symptoms, remains localised on the liver, and does not spread to the other parts of the body.
Cancers of the lymph nodes and lymphatic system are known as lymphomas. Lymphomas can affect many organs of the body but are commonly seen in peripheral lymph nodes (located deep in the subcutaneous layer of the skin).
These are often seen in older female dogs that are still intact (not neutered). As we all know, dogs have a total of ten teats which are distributed across the chest and abdomen in pairs of two. Mammary tumours occur most commonly in the last pair of teats. While it does most commonly affect females, there have been male dogs affected by mammary tumours as well.
Mast cell tumours or MCTs are a type of cancer that is made up of normal healthy cells that have grouped together and formed a mass. These tumours most commonly form on the skin but can also affect other parts of the body, including the respiratory and digestive tracts. In dogs, MCTs may be relatively benign and easily treatable with surgery. However, they can also be much more aggressive and spread to other parts of the body.
These are tumours originating from cells which are responsible for producing pigment. Although most commonly found as masses or lumps on the skin, these tumours have a high tendency to spread. They also have a higher tendency to bleed as they grow and spread.
These are tumours which affect the oral cavity and are among the most common type of oral tumours in dogs. Melanomas can develop on gums, lips or other parts of the mouth. They are malignant in nature and cause severe discomfort to dogs while eating.
Cancerous growth seen in bones. This is most often seen in long bones of the limb but does rarely affect the mandible or lower jaw and other bones of the skull.
This is a common type of cancer found in dogs comprising a variety of malignant tumours that affect the connective tissues of the body, such as fat, muscles and cartilage. They are usually present as non-painful lumps on various parts of the body such as limbs, chest or the abdominal wall. Soft tissue sarcomas can affect dogs of any gender, breed and age but are more common in older large-sized breeds.
As the name suggests, this kind of cancer affects male dogs and forms on the testicles. The most commonly affect male intact (unneutered) dogs over the age of 10 years. Cryptorchid dogs (those whose one or both testicles remain undescended) are more prone to testicular cancer as abdominal temperatures and conditions have a mutative effect on the undescended testes.
Thyroid cancer involves tumours that affect the thyroid, a gland in the neck responsible for releasing important hormones that regulate metabolism and help control major functions of the body. Thyroid tumours are almost always malignant and often spread to the lungs and lymph nodes They can also invade nearby structures such as the windpipe, blood vessels and oesophagus.
- Transmissible Venereal Tumours, also known as Venereal Granulomas:
Shortened to TVTs or VGs, these are an infectious, cancerous growth in dogs. The spread of the tumour is most often through mating or urinary contact, thus making it like an STD of dogs. It manifests as cauliflower-like growth on the genital organs. There are other unusual places where TVTs crop up like the eye or inside the mouth.
What Are the Common Types of Cancer in Cats?
Cancer is not as common in felines as it is in dogs, but they suffer from it. Here are some common types of cancer that have been medically diagnosed in cats.
This is commonly associated with the feline leukaemia virus (FeLV). Even though there are vaccines available against FeLV, there are still a majority of cats which develop lymphoma after exposure to the virus.
- Squamous Cell Carcinoma
- Fibrosarcoma
This is a kind of soft tissue sarcoma observed in soft tissues like muscles or connective tissue, associated with badly given injections, sometimes also known as injection-site sarcoma.
Much like in dogs, these are seen in older cats which have given birth to frequent litters.
- Cats are prone to other kinds of tumours such are lung tumours, brain tumours, nasal tumours and liver tumours, but these are not very common.
What Are the Known Causes of Cancer?
Cancer occurs when any sort of trigger causes the uncontained division and expansion of cells in the body, especially in their initial undefined stages. These triggers could be physical, chemical, or infectious in nature.
- Dogs, cats, cattle and horses with white or light coloured skin are known to develop squamous cell carcinomas more easily than other coat colours, especially with prolonged exposure to ultraviolet radiation.
- Environmental carcinogens, especially those found in cigarette smoke, have been shown to contribute to the development of oral carcinomas in cats.
- Sexually transmitted and spread through the circulation of sex hormones. For example, transmissible venereal tumours.
- Viruses have long been known to transmit certain kinds of cancers or growths, e.g. papilloma in dogs and cattle or feline leukaemia in cats.
- Hereditary factors may play a role in the transmission of mast cell tumours.
- Cancer occurs in older animals more frequently than younger ones. It is thought that the weakening of the immune system makes it easier for cells to mutate into precancerous cells.
So, What Are the Signs to Look Out For?
- Abnormal or rapidly growing swellings on the body
- Sores or wounds that do not heal
- Loss of appetite and weight loss
- Unexplained vomiting and diarrhoea
- A dramatic difference in coat quality
- Lethargy
- Bleeding or discharge from body openings
- Difficulty eating, swallowing, or breathing
- Lameness
- Difficulty urinating or defecating
Breeds That Are More Susceptible to Growths or Tumors:
- The heartbreaking news is that a very beloved breed, the Golden Retriever, develops cancers like hemangiosarcoma, lymphoma at higher rates than most other breeds, and this is attributed to poor breeding practices such as inbreeding.
- Cocker spaniels are more prone to anal sac cancers and mammary tumours.
- Poodles and terrier breeds have a higher predisposition for mammary tumours as well.
- Mast cell tumours are seen in breeds like the Boxer, Boston Terrier and Labrador Retriever, especially among older dogs.
- Soft tissue carcinomas occur mostly in older dogs of larger sized breeds like the Doberman, St Bernard and Golden Retriever.
- Hounds, collies, boxers and German shepherds are more susceptible to testicular cancer
- Beagles, boxers and golden retrievers are more prone to thyroid cancer.
- Perhaps a reason to rejoice is that mixed-breed dogs are less susceptible to cancer than their purebred counterparts.
- There is very little breed-specific data for incidence of cancer in cats. However, much like dogs, the pure breed group is more likely to develop cancers — chiefly among which are Persian and Siamese cats.
Briefly, Cancer in Birds:
As the average age of pet birds has increased, so has the observed incidence of growths and tumours. Their incidence and location are not all that different from those seen in other companion animals.
Internally, they may be afflicted by cancerous growths (lymphomas or carcinomas) on the liver, kidneys, ovaries, thyroid gland, pituitary gland, muscles and bones and stomach and not much may be observed in terms of clinical signs until the bird has passed away.
Squamous cell carcinomas or skin cancers may be observed around the eyes and beak, around the tips of wings and toes. Radiation therapy has helped in the treatment of these but to some small extent.
Lipomas or fat tumours are often seen on the breast tissue or keel bone of budgerigars. These are often harmless and may not need surgical intervention.
There are pituitary adenomas observed in budgerigars and cockatiels, which may lead to nervous symptoms like seizures and muscle spasms or may be indicative of excessive pituitary function like increased thirst and excretion of wastes.
Briefly, Cancer in Guinea Pigs:
Growths of many kinds have been observed and documented in guinea pigs, out of which the most common ones are pulmonary adenomas and cutaneous tumours.
These tumours can be detected through the presence of these signs such as the presence of lumps or bumps on the skin, lethargy, loss of appetite, poor hair coat, signs of pain on touching or picking up, and difficulty in breathing.
Definitive diagnoses of these tumours occur through blood tests, ultrasound, X-ray or biopsies.
What Are the Treatment Options for Cancer?
Options may include surgical treatment or combination therapy of surgery and chemotherapy, which you can best discuss with your veterinarian. The success of these varies. For example, amputation can be done for a dog suffering from osteosarcoma in one limb, and the animal can still expect to enjoy a good quality of life on its remaining limbs with very remote chances of recurrence of the osteosarcoma.
A combination of surgery (animal birth control) and chemotherapy is needed to reduce and stop the growth of TVTs, but there are cases where the tumour has recurred.
MCTs are best left untouched because even if a microscopic amount of tumorous tissue is left behind during a surgical excision, they grow back quickly and aggressively.
Palliative Care
This is a line of care and therapy done when a decision has been taken to withdraw the pursuit of any curative therapy for a life-limiting illness like cancer.
The first step in palliative care is to meet with your veterinarian and discuss the expected course and prognosis of the disease and its impact on your pet’s quality of life. Once an animal's activities of daily living have been identified, it’s important to define family beliefs, the family's needs as care unfolds, and the goals for the dog or cat or any other pet as the end approaches.
Pain management is the most important facet of palliative care in pets. Pain is best managed from a multimodal perspective, which means using various techniques, both pharmacologic (medications) as well as non-pharmacologic in conjunction to achieve the goal of maximum comfort. Homoeopathy, acupuncture, massage, therapeutic laser therapy, hydrotherapy and physical therapy are some non-pharmacological mediums which can alleviate pain and suffering.
Besides various therapies, you can make small adjustments in day-to-day life like replacing your normal floor surface with a non-skid material, raising the height of your pet’s food and water dishes, blocking access to stairs or carrying your pet or supervising them when they need to go upstairs or downstairs, or creating comfortable nooks in your place which your companion animal understands is their safe zone.
Finally, Let’s Talk About Diet
There is evidence to suggest that most kinds of cancer cells require high energy content derived from carbohydrates, high fructose fruits and vegetables with high starch content. So, if we want to prevent any neoplasia, we need to keep carb content low, while keeping the proportion of protein and good fats high. You may have to change your pet over to homemade food because commercial kibble is very rich in carbs.
Dogs’ diets can comprise a 50:50 ratio of meat protein to vegetables (vegetables such as leafy greens, carrots, zucchini, broccoli, and green beans are known to be good preventative foods against cancers). This proportion must be 80:20 in cats. Meat can include white meat such as chicken or turkey or fish, which is easy to break down and digest.
Sources of good fat include flaxseed oil, olive oil, coconut oil, fish oil or cod liver oil.
An important thing to keep in mind is that depending on where you live, the water supply that comes to your home may contain varying degrees of toxins or fluorides which may act as carcinogens. Be sure to give your pet filtered water in ceramic or metal dishes and avoid plastic utensils.
A life afflicted with cancer can be heart-wrenching for the victim as well as family, and I hope this piece helps you combat or be better equipped against this dreadful disorder and keep your pet comfortable and happy.