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July Cytology Month - Mast Cell Tumors Part 1

The most common skin tumor of dogs are Mast Cell tumors (MCT). They account for approximately 1/5 of all skin tumors in dogs. MCT can have very variable appearances and cannot be diagnosed without testing, usually via fine needle aspirate and microscopic examination (cytology) They have a very distinct appearance (round cells with cytoplasmic granules).

· The most common treatment is labwork, lymph node aspirates followed by surgical excision

· A more extensive work-up should be performed if it is not in an area where it can be easily surgically removed. This work-up would include thoracic radiographs, abdominal ultrasound including aspirates of the liver and spleen

· Once removed, the tumors are sent off for histopathology, which can grade the tumors. In the past, the Patnaik system was used that assigned Grade I-III, but more recently, the Kiupel system is used, which is based on the mitotic index

· Low grade MCT’s have a better survival time (approx. 2 years) compared to high grade MCT’s (MST is approximately 4 months)

· In the cases of either incompletely resected low-grade MCT, high grade tumors, or metastasis, the options include radiation therapy, tyrosine kinase inhibitors (such as Toceranib), chemotherapy and corticosteroids

· If excision is not possible (such as if the tumor is located in a difficult location, such as a distal limb, there is a intratumor injection available (Tigilanol tigate)


1) Veterinary Partner.

2) Tilley, L. P., & Smith, F. W. (2005). The 5-minute veterinary consult: Canine and feline. Philadelphia: Lippincott Williams & Wilkins.

3) Yin, S. A. (2010). The small animal veterinary nerdbook. Davis, CA: CattleDog Pub.

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