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
- 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
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.
In the next post, we’ll discuss what treatment of lymphoma in cats entails, what the prognosis is, and how to potentially prevent it in cats. Don’t despair if your cat was diagnosed with cancer, as there are options for treatment!