Surgical treatment of mast cell tumors in dogs

Surgical Treatment of Grade I and II Mast Cell Tumors in Dogs

Surgery is the treatment of choice for mast cell tumors in dogs.  Most dogs with single grade I Surgical treatment of mast cell tumors in dogsmast cell tumors (>90%) and grade II mast cell tumors (approximately 75%) have long survival times after complete surgical removal of their mast cell tumors.  Click here to learn about how veterinarians grade mast cell tumors in dogs.

It is commonly understood that mast cell tumors may look like a compact, focal mass, but that invariably, they have finger-like extensions into the surrounding tissue.  Due to these finger-like extensions of the tumor, it is important to take wide margins of tissue around the tumor to increase the likelihood of a complete excision.  One of the of the current recommendations for obtaining a complete excision of grade I and grade II mast cell tumors is to remove 2 times the diameter of the tumor up to 2-3 cm in each direction and obtain one deep facial plane below the tumor.  (Fascia is the connective tissue that layers the outside of muscle).  By removing a layer of muscle or fascia below the tumor, the potential for a complete excision of the mast cell tumor increases greatly.

One study concluded that if a mast cell tumor is removed with 2 cm lateral margins and one deep facial plane below the tumor, 91% of grade I and II mast cell tumors will be completely excised.  It also suggested that 1 cm margins were able to obtain tumor-free margins in 100% and 75% of grade I and II mast cell tumors, respectively.

Surgical Treatment of Grade III Mast Cell Tumors in Dogs

Guidelines for surgical removal of grade III mast cell tumors is less certain, as most studies haveMast cell tumors in dogs and surgical treatment evaluated outcome of surgical removal of grade I and grade II mast cell tumors.  Grade III mast cell tumors are more aggressive in behavior both locally and have the added risk of metastasis to other sites.  It is more likely wider margins are necessary for complete excision of grade III mast cell tumors and thus 3 cm lateral margins and a facial plane below are recommended.

Surgical Treatment for Dogs with Mast Cell Tumors of the Extremities

When mast cell tumors develop in the distal extremities (limbs), it is often difficult to obtain wide margins of resection of the mast cell tumor.  Wide lateral margins are difficult to obtain due to inability to close the skin without tension that can cause complications with tissue healing.  However, more self-limiting is the deep margin that is limited by the bony structures of the limb.  Complicated skin grafts do not solve this problem with the deep margins.  They may improve the width of the lateral margins, but don’t solve the limitations of obtaining deep margins.  As a result, skin grafts are rarely beneficial and may be difficult to heal.

A more practical approach is to take as wide margins as is reasonably possible and be prepared to follow with radiation therapy to treat what microscopic disease may be left behind if removal of the tumor appears to be incomplete.  Although an amputation is an option, it is not advised over surgical removal and radiation therapy, which has an 80% likelihood of preventing recurrence of the cancer.

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Dr Stephen Atwater

Stephen W. Atwater, DVM, MS, Diplomate ACVIM (oncology) is a board-certified veterinary oncology specialist. His professional interests include utilizing emerging therapies for difficult to treat cancers.

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