Neoplasia in Cats

Causes, Treatment, and Prevention

A tabby cat with a white chest and paws is sitting on someone's lap.


Neoplasia in cats is the abnormal growth of cells within the body. This condition can affect cats of all ages and breeds, but it is most commonly seen in older cats. This growth of cells can lead to malignant or benign tumors. The prognosis and treatment for benign and malignant neoplasms vary significantly. Benign neoplasms may not need to be treated at all, unless they interfere with bodily function, whereas many forms of malignant cancers require surgery, chemotherapy, radiation therapy, and supportive care like fluids, pain medications, and medications to treat nausea and increase appetite.

What is Neoplasia?

Neoplasia is a condition in which cells within a cat’s body divide and multiply at abnormally rapid rates, leading to visible lumps under the skin or internal growths that may not be readily evident. These aberrant cells can cause solid masses of abnormal tissue, called tumors, or may infiltrate normal organs, skin, nerve, bone, and connective tissue.  

Neoplasia can be malignant or benign. Cancer is the term commonly used for malignant neoplasia, which may aggressively invade other areas of the body and cause underlying tissue destruction, inflammation, loss of function, and tissue death. Malignant neoplasia may also spread to other organs, like the lungs, in a process called metastasis. Benign neoplasia does not generally invade and destroy local tissues or spread throughout the body. Neoplasia can affect cats of all ages and breeds, although it is more common in middle-aged and older cats.

Types of Neoplasia in Cats

There are many forms of neoplasia that can develop in various parts of a cat's body, and some are more serious than others. Some common forms of neoplasia include:


Lymphoma is a cancer affecting a type of white blood cells called lymphocytes that play a role in immune function, and there are many different types of lymphoma which carry different prognoses. Lymphoma can affect various areas of the body. A large majority of lymphoma cases in cats affect the GI system. A recent study in cats found that renal lymphoma occurred in just under 4 percent of lymphoma cases in cats from one retrospective study. Lymphoma is the most common form of malignant neoplasia in cats and represents up to nearly 30 percent of all tumors diagnosed in cats in the United Kingdom.

Squamous Cell Carcinoma

Another serious, common neoplasia in cats is squamous cell carcinoma (SCC), which is a very aggressive type of cancer that often occurs inside cats' mouths. SCC is the most common type of oral tumor in cats (75 percent approximately). Unless caught and addressed very early, it can be very difficult to treat this time of cancer, even with surgery and radiation. These cats may show signs of drooling and loss of appetite.

Injection Site Sarcoma

Injection site sarcomas can develop after a cat receives an injection, sometimes even developing years after the injection. These are very rare reactions (one in 10,000-30,000), where local tumor development occurs. These tumors are aggressive and early intervention and prompt examination of any lumps arising from an injection area is key to identifying and treating this type of tumor.

While not fully understood, it is thought that these tumors occur as a result of an inflammatory reaction to additives in vaccines in some cats but not necessarily a direct result of injection to the vaccine itself. Your veterinarian carefully helps to determine which vaccines are needed for your cat so as to minimize this risk, will choose feline-safe vaccines, and also will choose specific sites to place vaccines with this in mind. The benefits of these vaccines far outweigh this risk.

Mast Call Tumors

Mast cell tumors occur when another type of white blood cells, mast cells, begin growing abnormally and invading other tissues. They can occur in the skin, spleen, and gastrointestinal tract. Around 20 percent of skin tumors diagnosed in cats are mast cell tumors.  


Trichoblastomas are one type common benign skin tumors in cats and are not generally associated with symptoms of illness. For any new lumps, your cat should be assessed by a veterinarian, as most of these can be difficult to differentiate just by looking at them. For many malignant cancers, cats may appear to be sick, but may often hide signs until it is progressed. Weight loss, vomiting, lethargy and diarrhea are some of the most common symptoms observed.

Other Forms of Cancer

Cats may also suffer from cancers of the mammary glands, bones, lungs, and nervous system and these may show a variety of symptoms, including pain, swelling, and seizures. Cats that are not spayed generally have a much higher incidence of mammary tumors, which can be quite aggressive but start as a small mass on the skin or abdomen of the cat.

Symptoms of Neoplasia in Cats

The symptoms of neoplasia very much depend on the location of the abnormal cells, the type of cells affected, and the body systems affected. A cat with malignant neoplasia may show many of these symptoms, some of them, or none of them. Any illness or change in behavior should be assessed by a veterinarian.


  • Weight loss
  • Loss of appetite
  • Lethargy
  • Vomiting
  • Diarrhea
  • Visible masses or tumors 
  • Enlarged spleen or other organs
  • Fluid in the abdomen

Weight Loss

Cats with malignant cancer may lose weight because their appetite is decreased due to nausea, pain, or a general feeling of malaise caused by the growth and spread of the abnormal cells. However, because neoplasia can interfere with a cat's ability to digest and utilize nutrients from food, sometimes cats may have voracious appetites yet still be losing weight. In these cases, weight loss despite continued food consumption may be the only visible symptom that something is wrong.

Loss of Appetite

Cats may stop eating due to nausea, pain, and feeling poorly overall. If neoplasia is affecting the stomach, intestines, mouth, or face, it may be too difficult and uncomfortable to chew, swallow, and/or digest food.


If cats are not acquiring enough nutrients and energy from food, either from loss of appetite or the inability to eat, they will become lethargic. A lethargic cat may sleep for longer periods or at unusual times, hide under beds or in closets, and be reluctant to interact with others and perform normal activities like playing or climbing.


Tumors of the gastrointestinal tract commonly cause vomiting in cats, because normal digestive processes cannot occur. Tumors can also cause obstructions which can lead to vomiting. Vomiting may appear suddenly or cats may vomit for months or even years. Chronic vomiting is often associated with gastrointestinal lymphoma.


Diarrhea may result from altered and/or impaired function of the intestinal lining, particularly if cancerous cells are present along the gastrointestinal tract. It may also occur due to an inability to properly digest food or an intestinal blockage.

Visible Masses or Tumors

Cats with neoplasia may have lumps under the skin or fur that can be seen or felt. Because it is not possible to determine if a lump is malignant or not just by looking at it, any appearance of tumors or lumps on a cat should be checked out by a veterinarian.

Enlarged Spleen or Other Organs

When cancer cells infiltrate internal organs, they may enlarge. A veterinarian can often detect an enlarged spleen, liver, or kidneys when performing abdominal palpation during a physical examination or with X-rays. You may also be able to detect enlarged organs simply while petting your cat, if your cat is very thin, or has lost a lot of weight.

Fluid in the Abdomen

Cats with cancer may build up fluid in their abdomen, which can exert pressure on their lungs and other organs. They may show difficulty breathing, a large, distended abdomen, and reluctance to move or do any activity.

Causes of Neoplasia

Like in humans, it is often difficult to determine why neoplasia develops.

  • Certain viruses, like feline leukemia virus (FELV) and feline immunodeficiency virus (FIV), can lead to the development of cancer.
  • Genetics may be another cause contributing to certain cancers, and environmental factors and diet may also play a role.
  • Exposure to chemicals, carcinogens, and pollutants may be contributing factors. Tobacco smoke is one possible carcinogen that may promote the development of cancer.

Diagnosing Neoplasia in Cats

Your veterinarian will begin with a thorough physical examination of your cat, and depending on what type of neoplasia is suspected, will likely order additional tests. These tests include bloodwork to look for abnormalities in white blood cells, kidney function, and any potential liver damage. Your cat may also be tested for FELV and FIV. Sometimes specialized blood tests are used to further characterize any abnormalities.

Abdominal and chest X-rays and ultrasounds can sometimes determine if organs are abnormal or metastasis is present. If enlarged lymph nodes or masses are detected in the skin, your veterinarian may recommend taking a sample with a needle or putting your cat under anesthesia for a biopsy of the area.

If chronic diarrhea is an issue, a fecal examination and gastrointestinal panel to rule out parasites and other sources of diarrhea may be performed. If intestinal or stomach cancer is suspected, a veterinarian may recommend an ultrasound and/or intestinal biopsy.

If neurological symptoms are present, an MRI or CT scan may be performed.


Treatment depends on the type of neoplasia present and how serious it is. If it is a benign growth that isn't bothering the cat, nothing may need to be done about it. If it is an aggressive and malignant tumor, often removing it surgically, along with wide margins of surrounding tissue, is indicated. Depending on the type of tumor, surgery may need to be followed up with chemotherapy or radiation therapy.

Some cancers may be curable, depending on type and location. Often, the most common cancers like lymphoma are not, but they can be put into remission, which means your cat can have a good quality of life while the cancer is kept under control.

If malignant neoplasia is widespread and/or very aggressive, palliative care may be the only option or the most humane option for your cat. In this case, the cat is made comfortable and pain-free for as long as possible until it is time to say goodbye.

Prognosis for Cats with Neoplasia

Prognosis depends on the type of neoplasia, where it's located, and whether it's malignant or benign. Benign neoplasms have a good prognosis, while aggressive, metastatic cancers have a poor prognosis. Cats with cancer may survive for weeks, months, or years after diagnosis. With malignant cancers, the goal may not be to cure the cancer, as this may not be possible, but rather to improve the quality and duration of life and prevent suffering.

In the case of lymphoma, depending on the type, chemotherapy improves the prognosis and many cats respond well. As many as 50-80 percent of cats may achieve remission of clinical signs with chemotherapy for lymphoma for four to nine months.

How to Prevent Neoplasia

Because in most cases the cause of neoplasia is not known, there is no surefire way to prevent it. Some precautions can be taken, like spaying your cat, not exposing your cat to tobacco smoke and other toxins, keeping your cat indoors and vaccinating to help prevent infection with viruses like FELV and FIV, and reducing household stress. However, if your cat does develop cancer, know that is it not your fault and there are many factors that determine whether or not malignant neoplasia occurs.

Catching cancer early and treating it quickly is one of the most important steps you can take for your cat. Schedule regular veterinary examinations, including routine bloodwork, and have any unusual changes or symptoms of illness checked out right away.

If you suspect your pet is sick, call your vet immediately. For health-related questions, always consult your veterinarian, as they have examined your pet, know the pet's health history, and can make the best recommendations for your pet.
Article Sources
The Spruce Pets uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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