One of the top three killers of geriatric cats is cancer. Sadly, as cats live longer (thanks to improvements in quality of care, better nutrition, and preventative care), they often succumb to cancer as they age. There are several types of cancer in cats, and one that I see the most is lymphoma in cats.
What is lymphoma in cats?
Lymphoma, similar to non-Hodgkins lymphoma (NHL) in humans, is an aggressive cancer typically of the lymphatic system (e.g., the lymph nodes, thymus gland, white blood cells called lymphocytes) and can affect multiple organs. It’s one of the most common types of cancer that I see in the veterinary emergency room, and can be frustrating to diagnose.
While lymphoma cells can grow anywhere in the body, the three most common body systems that can be affected by lymphoma include:
- The lymphatic system, including the lymph nodes and lymph-tissues throughout the body; this is also often called the multicentric form
- The gastrointestinal (GI) tract, including the stomach, small intestines, and, rarely, colon
- The mediastinum, or the space in front of the heart, surrounding the aorta and other important vessels in the chest
In my experience, GI lymphoma is the most common type of cancer in cats nowadays. There is an association between inflammation and the development of lymphoma. Cats that have inflammatory bowel disease (IBD) may be at risk for development of GI lymphoma. (This is one of the reasons why your cat’s chronic vomiting and diarrhea needs to be diagnosed and treated sooner than later!).
Decades ago, the most common type of lymphoma used to be mediastinal lymphoma—this was more common due to the prevalence of FeLV, or feline leukemia (which is associated with an increased risk of cancer); however, thanks to blood screening and vaccination, feline leukemia is less frequently seen.
While less common, lymphoma can also present in other parts of the body, including the airway (nose, larynx, trachea), kidneys, central nervous system (brain, spinal cord), skin (e.g., cutaneous), and peripheral lymph nodes.
Two types of lymphoma in cats
There are two main types of lymphoma:
- Low-grade (small cell) lymphoma
- High-grade (large cell) lymphoma
These two types of cancer act very differently. Low-grade or small cell lymphoma most commonly affects the GI tract, and grows more slowly. Because it is slower growing, oral chemotherapy drugs (e.g., prednisolone, chlorambucil) are typically used with this type of lymphoma. While it can take almost a month before cats will start to show response to oral chemotherapy, almost 90% of cats will respond to treatment. Survival time is longer for low-grade lymphoma, with an average survival of 1.5 to 2 years.
High-grade or large cell lymphoma is more aggressive, but the goal is to kill the cancer cells and induce “remission” (meaning the cancer cells have disappeared temporarily). High-grade lymphoma requires chemotherapy (both injections and orally administered chemotherapy such as L-asparaginase, vincristine, doxorubicin, cyclophosphamide, prednisolone, etc.). Sometimes, radiation therapy or even surgery may be necessary. While complete remission can be achieved in 50-75% of cats, the average survival for cats is shorter with high-grade lymphoma—about 6-9 months. Eventually, cats will come out of remission, and may become insensitive to chemotherapy and no longer respond to therapy. In the next post, I’ll review treatment and prognosis in more detail.
Clinical signs of lymphoma in cats
So, what are signs of lymphoma in cats? Clinical signs may vary, depending on what organs are affected. Signs of lymphoma can mimic other underlying medical problems, so a veterinary visit and thorough examination is a must. Signs of cancer in cats may be subtler and more chronic and include:
- Not eating
- Hiding
- Lethargy
- Weight loss
- Increased respiratory rate/difficulty breathing
- Frequent vomiting
- Diarrhea/softer stool than normal (e.g., pudding consistency)
- Swelling under the skin or unusual lumps or bumps on the body
- Death
How does my veterinarian diagnose lymphoma?
Unfortunately, there’s no single simple test for lymphoma. Your veterinarian will need to do several tests such as:
- A thorough physical examination
- A complete blood count (to look at the white and red blood cells, platelet count, etc.)
- A biochemistry panel (to look at the kidney and liver function, protein, salt balance, blood sugar, etc.)
- A urine test
- X-rays of the chest/lungs/heart and abdomen (to look at the size and shape of certain organs)
- Abdominal ultrasound (to look at the architecture of the organs)
- Fine-needle aspirates (FNA) of cells (cytology) of any abnormalities found on ultrasound; this is often of abdominal lymph nodes or thickened or enlarged organs
- Biopsies may be necessary if the fine-needle aspirates did not reveal any obvious answer; this typically requires general anesthesia and removal of actual tissue, not cells (as done with an FNA)
- Surgery may sometimes be necessary to confirm a diagnosis or to help with initial treatment; full thickness biopsies of intestines is warranted
More advanced diagnostic tests like immunophenotyping (e.g., done through flow cytometry or immunohistochemistry) or PCR for Antigen Receptor Rearrangement (PARR) may be necessary. These aren’t common tests that your veterinarian would be performing, but rather tests that a veterinary oncologist may do if you are pursuing chemotherapy. These advanced tests may be helpful if the other (above) tests don’t yield a definitive diagnosis of lymphoma but is still suspected. The tests help look for certain markers on the cells and where the cancer cells may be coming from (e.g., clonal population), and often help determine outcome and prognosis.
Should you see a veterinary oncologist?
First, please know that the diagnosis of lymphoma is not always a “death sentence.” In fact, lymphoma—while one of the most common cancers diagnosed in dogs and cats—has one of the best prognoses with treatment. Most people have had a previous experience with chemotherapy in their human family members or friends, and often have a “bad” memory of it. Hair loss, nausea, weight loss, loss of appetite—all the bad things that come with chemotherapy. However, in veterinary medicine, it’s a bit different. In veterinary medicine, we don’t aim for cure, as it typically makes our pets too sick. Instead, our goal is to try to shrink cancer cells while preserving qualify of life.
My advice? It’s worth making an appointment with a board-certified veterinary oncologist so you can directly talk to them about treatment options. Making that $150 appointment doesn't commit you to chemotherapy. You don’t have to necessarily spend thousands of dollars or put your cat through anything you don’t want to. That said, it’s worth making that first appointment so you can hear their opinion of the cancer and treatment options. That way you are the most informed about your pet’s medical care.
What’s the treatment for feline lymphoma?
Thankfully, of all the types of cancer in veterinary medicine, lymphoma is the one that best responds to treatment. Treatment may include:
- Chemotherapy (both oral medications at home and injections at the vet clinic)
- Surgery, rarely, if there is a large mass or obstruction
- Radiation therapy, rarely, for nasal, central nervous system, and laryngeal lymphoma
In veterinary medicine, most types of lymphoma in cats are treated with a “CHOP-based” protocol. This consists of rotating injections of chemotherapy, which is generally weekly for 4-5 weeks (called a cycle). Specifically, we use drugs like vincristine/vinblastine, cyclophosphamide, doxorubicin, and L-asparaginase. This typically occurs for 19-25 weeks. Simultaneously, you have to give oral prednisolone (a corticosteroid) at home.
How do cats handle chemotherapy?
So, do cats handle chemotherapy well? The biggest side effects are loss of appetite, nausea, and mild loss of fur (often whiskers). Very rarely, cats will experience immunosuppression and bone marrow suppression. In fact, side effects of treatment are generally mild and occur about 10-20% of the time. The majority of the time, the side effects can be easily treated with fluids under the skin, anti-nausea and anti-vomiting medication, and even appetite stimulants (like mirtazapine or Entyce™).
What’s the prognosis for feline lymphoma?
Unfortunately, the long-term prognosis for feline lymphoma is extremely variable based on which form of lymphoma your cat may have. In basic terms, we tend to say “large cell” and “small cell” lymphoma. Large cell, also known as lymphoblastic or high-grade lymphoma, is the more aggressive type and generally affects the gastrointestinal tract. Small cell, also known as well-differentiated lymphoma or low-grade lymphoma, also affects the gastrointestinal tract but is less aggressive in nature.
While cancer isn’t curable in veterinary medicine, some cats can live for up to 1-2 years, depending on the type of lymphoma. Large cell lymphoma generally has a prognosis of 6 months. Small cell lymphoma generally has a prognosis of 2 years.
The prognosis for lymphoma will also vary based on where the lymphoma is in the body, concurrent disease (such as concurrent feline leukemia), and response to chemotherapy. Some rarer cats can even go into remission, where they may not require chemotherapy during that time period.
Can I prevent cancer in my cats?
There are only a few known ways of preventing feline lymphoma. The first is to make sure your cat is negative for FeLV and stays indoors to avoid exposure from other cats. Vaccination against FeLV isn’t 100% effective, but can reduce the severity of FeLV.
As a toxicologist, I also want you to minimize any obvious exposure to tobacco smoke and any other chemicals that are known to be carcinogenic. (Contact the ASPCA Animal Poison Control Center or your veterinarian for more information.) While there’s not a definitive link to this, we veterinarians suspect that exposure to environmental poisons can potentially increase risks of cancer. Lastly, get to your veterinarian every year with your cat. The sooner we detect cancer on physical examination, the sooner we can treat it, and potentially the better the chances for survival.
