Cats, just like humans and any other animal, can have cancer during their lifetime. Molecularly speaking, cancer in cats develops because something within a single cell of their body went wrong. This is often a change in the cell’s DNA, or a change that affects how well a cell can grow and divide. Once that process starts, it is hard to stop it. Cancer cells will keep growing and multiplying, forming bigger and bigger masses that can spread throughout the body, impede organs’ functions and, after a while, can be lethal.
Here I want to offer a glimpse into the recent research done to understand and treat cancer in domestic cats.
What is cancer in cats?
Cancer is a disease that can occur anywhere in the cat’s body. It can happen because of something that was already in the cat’s genetic makeup, or because something happened during your pet’s lifetime.
Breed-based risks of cancer
Among the large family of domestic cats, there is a lot of genetic variability. This is what makes some cats smaller, some larger, some with a short hair, some with no hair, some with pointy ears and some with smushed faces. Consequently, it translates into a different risk for cats to get cancer, and what kind of cancer they can develop.
A retrospective study on 1,129 cats published in the Journal of the American Animal Health Association evaluated the frequency at which cancers occur in cats, and across breeds (J Am Anim Hosp Assoc. 2011 Jan-Feb;47(1):28-36).
The three most common types of cancer in this study were:
- Lymphoma: This is a type of blood cancer that develops in the lymph nodes and causes them to swell. It is one of the most common cancers diagnosed in cats and can be caused by conditions such as the Feline Leukemia Virus (FeLV).
- Adenocarcinoma: This is a general term used to indicate tumors that develop from the mucus-producing glandular cells of the body. These tumors are then further broken down based on where they originate. For example, you can have adenocarcinoma, in the lung, intestine, breast and so on.
- Mast Cell Tumors: These are tumors that can develop from mast cells, which are a type of white blood cell. While many of these tumors are benign, they can also be malignant. Since they are in the blood, they can reach and keep growing in different organs, often causing organ failure.
Other cancer types that are still common in cats include:
- Squamous Cell Carcinoma (SCC): This is a type of skin cancer that typically develops on exposed skin, such as on the ears, nose, and eyelids, especially in white cats in sunny climates. It is another common type of feline cancer.
- Fibrosarcoma: This is a cancer of the soft tissue. This tumor type is slow to spread to other parts of the body, but is locally aggressive, aka likely to stay in one spot.
- Mammary Tumors: Mammary (breast) cancer is another common cancer in cats. Almost 90% of feline mammary tumors are malignant, meaning they have the potential to spread to other parts of the body.
- Bone Cancer: Bone cancer is also common in cats, but it is not as prevalent as the other types mentioned above.
In terms of breeds, some breeds are more likely to develop specific cancer types.
Russian blue cats, Siamese, and Maine Coon cats are more than three times likely to develop intestinal cancers compared to other breeds. Interestingly, there is also an increased risk of developing cancer in cats that are spayed or neutered when compared to intact pets.
What are the causes of cancer in cats?
Cancer can be caused by two main factors: genetics and environmental.
Genetic factors are the things that are either part of the breed or part of the cat’s family. This would include the cat’s mom and dad, and other “litter relatives” already having had cancer. We cannot do anything to change those, and it doesn’t matter how well the cat eats and exercises, these will not change the genetic driving these events.
Environmental factors instead include lifestyle and all the things that are present where the cat lives. These are the aspects that we have the option to change, with the goal, hopefully, to improving our feline’s friend’s lives.
Genetic causes:
- Hereditary predisposition: Cats from families or litters that have developed cancer may be at a higher risk for cancer. However, it’s not always easy to identify a cat’s family history, so many pet owners aren’t aware of this genetic link.
- Breed: While the links between cat breeds and cancer are not as strong as in dogs, it is suspected that purebred cats may be more susceptible to cancer than non-purebred cats.
- Viral infections: While not strictly a genetic cause, some viral infections in cats can cause cancer because they affect how cells are working. The Feline Leukemia Virus (FeLV) is a well-known example. FeLV can infect the blood-producing cells of the bone marrow, leading to the development of leukemia or lymphoma. Another example is the Domestic cat hepadnavirus (DCH), that also appears to be linked to an increased risk of lymphoma. In fact, a study on more than 700 cats reported that most of the cats with lymphoma were also positive for DCH (Vet Q. 2023; 43(1): 1–10).
Thanks to the new DNA sequencing technologies, scientists can study the genetics of cancer in cats to understand the cellular and molecular mechanisms behind it.
Researchers from the College of Veterinary Medicine at Chungbuk National University in Korea, published a recent study that summarizes the advanced in profiling the molecular mechanisms linked with cancer in dogs and cats (J Vet Sci. 2023 Sep; 24(5)). In cats, they highlight the connection between the presence of a specific RNA molecule, miR-219, miR-124 and miR-192, and the development of brain cancer.
Environmental causes
Similarly to humans, cats can be victims of the environment in which they live. Continuous exposure to dangerous factors can damage cells in such a way that they start growing uncontrollably, often leading to cancer.
Some of the most common environmental causes of cancer in cats are:
- Cigarette smoke: I know, you have never seen a cat lighting a cigarette. However, exposure to environmental tobacco smoke has been associated with an increased risk of developing oral squamous cell carcinoma (SCC) and lymphoma in cats. A study published in the American Journal of Epidemiology demonstrated that, overall, cats who live in a household with smokers, are 2.4 times more likely to develop cancer. Moreover, cats that have lived for more than 5 years in a smoke-polluted environment, are 3.2 times more likely to develop cancer.
This can happen not only because they inhale the particles, but also because cats like self-grooming. And when they do, toxic particles that are licked off their fur contribute to the damage that can cause tumor cells to form and grow. - Sunlight exposure: In cats, SCC (squamous cell carcinoma) is one of the most common skin cancers, and like in humans, it often happens in areas of the body that are easily exposed, such as the ears, eyelids, and nose. Prolonged exposure to UV radiation from sunlight is a risk factor for the development of cancer, particularly in white or lightly pigmented cats, is susceptible to the damaging effects of UV radiation.
- Chemical exposure: Exposure to herbicides, insecticides, household cleaners, and pesticides can be toxic to cats and may contribute to the development of cancer.
- Diet and exercise: Yes, just like in humans. Although not directly environmental, diet and exercise are factors that can heavily influence the risk of cancer in cats. A study published in 2017 in the Journal of Comparative Biology highlights how obesity is a strong risk factor for the development of cancer in pets (J Comp Pathol. 2017 May;156(4):296-309). This is mostly due to a hormonal imbalance caused by fat deposits, and by the lower ability of the immune system to fight cancer (and infections) in obese subjects.
Can you treat cancer in cats?
Now you know more about what causes cancer in cats…but can you actually treat it? This is a more challenging point, mostly because there is no as much literature as in humans or dogs. Yet, there are common elements between how cancer is treated in humans and pets.
- The earlier the better. The earlier a cancer is discovered, the higher are the chances of your cat to survive.
- The younger the better. Older cats have an array of health issues because of the advanced age, and they are less likely to make a full recovery from an aggressive disease like cancer than a younger cat would.
- Location matters. A tumor mass in the skin will be much easier, and cheaper, to remove than a mass in the brain or heart.
Chemotherapy
Excluding palliative care, there are treatment options that aim to kill cancer cells by disrupting some of their weak points. Most of these molecules go under the umbrella of chemotherapy, yet, they work in different ways.
Generally speaking, chemo drugs work by targeting rapidly dividing cancer cells. Cancer cells grow and divide much more quickly than healthy cells, and this “weakness” is often used fo therapeutic purposes.
The types of chemotherapy drugs used in cats can be categorized based on their biochemical mechanism of action:
- Alkylating Agents. Alkylating agents are a class of chemotherapy drugs that interfere with DNA replication in cancer cells, causing cell death. These agents can affect both cancerous and normal cells, which can lead to side effects.
- Antimetabolites. Antimetabolites, such as cytosine arabinoside and 5-fluorouracil, mimic the building blocks of DNA and RNA. By integrating into the DNA or RNA during replication, these drugs prevent cancer cells from growing and dividing.
- Mitotic Inhibitors. They work by disrupting how cells divide, and block them in a specific moment called mitosis phase. By preventing the cancer cells from successfully dividing, these drugs aim to reduce the growth and spread of tumors.
- Antineoplastic Antibiotics. Antineoplastic antibiotics are another group of chemotherapy drugs that bind to DNA, causing breaks in DNA strands. This triggers signals inside the cell that force it to die.
Targeted and Experimental Drugs
Drugs that are able to target a specific protein in a cancer cell can be called targeted drugs. They are often used in cancers where the care provider is sure about the presence of these targets in malignant cells.
For example, hormonal and Anti-Hormonal drugs are used in certain types of cancer that are caused by an exaggerated response to hormones in the body. In this situation, normal cells are hyperstimulated and start growing uncontrollably. These drugs can slow down or stop the growth of hormone-dependent tumors.
Another interesting kind of targeted drugs are biologicals. Biologicals are molecules that could be made of cells, or of things that a cell can produce. Monoclonal antibodies are Y-shaped molecules made by immune cells to attack specific targets. If cancer cells have these targets, that can also be called biomarkers, then monoclonal antibodies can help killing them.
An example of an experimental biological drug for cancer in cats is the one developed by researches from a multi-site project in Japan. They developed a monoclonal antibody that targets feline PD1 (Scientific Reports,13, 6420 (2023)) that effectively mimics the human drug Nivolumab, aka Opdivo. PD1 is a receptor present on the surface of immune cells that can fight cancer. When there is a lot of PD1, immune cells don’t work well. By blocking PD1, immune cells are re-activated and can now hunt down and kill cancer cells more efficiently.
A second example of an experimental drug is another monoclonal antibody that targets feline EGFR (Front Vet Sci. 2022 Nov 17:9). EGFR is a receptor on the surface of cells that can send improper signals inside the cell, telling it to grow and multiply. EGFR inhibitors are already used in human cancers such those in lung, pancreas and breast (Int J Mol Sci. 2023 Feb; 24(3): 2651).
Conclusions
Cancer cells are very smart and very ruthless. They can change and evolve over time to sneak away from drugs, and can keep growing and become lethal for cats. Yet, there is no much difference between cats and humans when it comes to cancer. They develop in similar ways and caused by similar things.
If your cat experiences changes in behaviors, lethargy, or you feel an unexpected lump when petting it, please call your vet immediately to discuss the best plan of action.
However, there are clear difficulties in fully understanding how drugs can treat cancer in cats. Things like the lack of large scale studies, limited funding, not-so-good-and-precise feedback from pet parents, and high costs are some of the challenges that have to be faced when thinking about this disease.
While difficult to handle as a news, cancer in cats is quite common. And it can be treated, or managed, too. Hopefully, here you were able to get a better grasp on the concepts around cancer. That’s because a knowledgeable pet parent, is a remarkable pet parent!
Biography
Seb Battaglia is a PhD scientist who spent the last 20 years of his life studying cancer. He worked in labs across Europe and the US, and published more than 40 peer-review research papers to date.
Seb is also an entrepreneur who owns My Blissful Pet. With My Blissful pet, Seb wants to help pets and pet parents alike by offering natural and crafted CBD products for pets, and by creating educational material to explain the science behind CBD for dogs and cats.
His website is https://myblissfulpet.com.
