Mast cell tumour in cats

Mast Cell Tumours in Cats-Symptoms, Diagnosis & Treatment

Mast cell tumours in cats

Also known as a mastocytoma, mast cell tumours (MCT’s) are skin tumours which have arisen from mast cells, which are a type of white blood cell formed in the bone marrow. Mast cells are found throughout the body, but are concentrated at points of contact between the cat and the outside world, especially the skin, respiratory tract, gastrointestinal tract, and conjunctiva.

Mast cell tumours can develop in different areas including the skin (dermal),  or internally (such as the spleen, liver or gastrointestinal tract),  known as visceral or disseminated. Cutaneous tumours can in some cases, spread to regional lymph nodes and on to the internal organs (most commonly the spleen or liver), or tumours can develop in the organs with no skin involvement. Highly aggressive tumours can enter bone marrow (which makes all of the blood cells) and turn up in the bloodstream.

Mast cell tumours are the second most common skin tumour in cats, the most common splenic tumour and the third most common type of intestinal tumour. The majority of mast cell tumours are benign (non-spreading) but up to 10%  are malignant (which can spread to other parts of the body).

Mast cells:

Mast cells are a part of the immune system and are involved in the inflammatory process and are responsible for the allergic reactions many people (and animals) experience. They do this by releasing granules, known as degranulation. Granules contain a number of active substances which perform the following functions:

  • Histamine – Vasodilation (widening of the blood vessels), increase vascular permeability and stimulates the nerve ending.
  • Heparin – Prevents the formation of blood clots.

If the cat (or person) has experienced an injury or a pathogen, degranulation is a good thing, but sometimes mast cells respond to normally harmless substances, such as pollen, inducing the allergy-related symptoms such as hives and itchy skin.


The cause is unknown, but it thought there is a genetic component because of a high incidence in Siamese cats.



  • Single or multiple hairless nodules (lumps) on or beneath the skin. They can occur anywhere on the body including the head, neck, torso, limbs and anogenital region. Tumours range in size from 1 to 4 cm and can wax and wane in size. They can be well defined or ill-defined. Ill-defined tumours are more aggressive.
  • From time to time nodules may become itchy and inflamed, due to the release of histamine from the tumour.
  • Up to 25% of tumours may have some degree of ulceration due to self-trauma.


Systemic symptoms may present with cats who have visceral mast cell tumours, which may include:


Your veterinarian will perform a physical examination and obtain a medical history from you. Tests will be necessary to diagnose mast cell tumour, these may include:

  • Fine needle aspirate (insertion of a needle into the tumour and drawing out cells) and cytology ( a study of the cells under a microscope). This applies to both cutaneous and visceral mast cell tumours, however sedation and ultrasound guidance are required to obtain a fine needle aspirate from an internal organ. Your veterinarian may also take samples from local lymph nodes to determine if the tumour has spread.
  • X-rays and ultrasound of the chest and abdomen to look for visceral tumours and liver or spleen enlargement.
  • Baseline tests including biochemical profile, complete blood count, and urinalysis to evaluate the overall health of your cat.
  • Biopsy and histopathology (microscopic examination of the biopsied tissue). The sample will be graded (or staged) at this time. Biopsy is usually carried out as both a diagnostic and a treatment.
  • Buffy coat examination. A sample of blood is spun at high speed to separate it into its components, red blood cells at the bottom, a small band of white blood cells and finally, the plasma. White blood cells are examined for the presence of abnormal mast cells.
  • Antihistamines will be administered prior to fine needle aspirate or biopsy as manipulation of masses can stimulate degranulation and cause mast cells to release large amounts of histamines causing inflammation, this is known as Darier’s sign.

Staging is necessary to determine the extent of the disease, there are three grades.

  1. Well-differentiated
  2. Moderately differentiated
  3. Poorly differentiated.


Surgery with a 2-3 cm margin to remove cutaneous tumours is the treatment of choice.

Visceral mast cell tumours can be more difficult to treat, if the spleen is affected, surgical removal can offer a cure.

Chemotherapy may be indicated as a follow up treatment for grade 3 tumours, to shrink tumours which can not be removed or target cancerous mast cells remaining in the blood.

Radiation therapy to treat tumours which can not be removed with wide enough margins, such as the limbs.

Antihistamines can be given to relieve symptoms associated with increased levels of histamine from non-treatable tumours.

Home care:

Your cat will be discharged with an Elizabethan collar to prevent self-trauma of the surgery site.

Antibiotics, painkillers, and antihistamines will be given to relieve symptoms.

Keep a close eye on the surgery site and if you notice any swelling, redness or oozing, speak to your veterinarian.