Mast Cell Tumours

- By Dr Charles Webb

Mast cells are part of the normal immune system and act as a defense against parasites. They are found within tissues that interact with the external environment such as the skin, respiratory and the intestinal tract. The mast cell contain granules of inflammatory biochemicals that are released to work against invading parasites. Unfortunately mast cells can be stimulated with other antigens that are of similar in size and shape to parasitic antigens. The mast cell responds by releasing biochemicals that produce localised redness, itchiness and swelling.

Frequently mast cells can form a tumour made of a cluster of many mast cells. Mast Cell Tumours (MCT) are unstable and release toxic granules with simple contact or even at random. They can be invasive and difficult to treat. The visible margin of the tumour is rarely the actual margin, they tend to have microscopic cells in the periphery that cannot be seen with the naked eye. When removing a MCT the excision must be broad and deep enough to get all of the tumour and the microscopic cells in the periphery. Often this results in a large excision and sometimes the tumour is located on a part of the body where obtaining adequate margins is not possible.

MCTs are the most common skin tumour in dogs, up to 21 percent of all canine skin tumours are MCTs and any breed dog can develop a MCT. Diagnosis can often be made with a needle aspirate. Your veterinarian will collects some tumour cells examine them under a microscope. Mast cells have distinct staining characteristics and are easy to recognise. Unfortunately though a tissue biopsy is needed to grade the tumour to determining prognosis and help your veterinarian determine the most appropriate treatment plan. Pathologists use The Patnaik System and the Kiupel System to grade MCTs. The Patnaik system grades tumours either I, II, or III. Grade I are considered benign and removal is usually curative, Grade III are malignant, while Grade II can go either way. Early detection and treatment is crucial especially when it comes to Grade II or III MCTs. The Kiupel system classifies MCTs as low grade or high grade with high grade tumours far more likely to behave metastasis. Surgical removal of low grade MCTs is often curative. Median survival time of greater than two years have been observed but some tumours that behave aggressively despite their low grade. High grade MCTs have a poor prognosis with survival times of less than four months. They behave aggressively and require more aggressive therapy.

Therapy for MCTs usually begins with surgery followed by chemotherapy, radiation therapy or both. The combination is chosen depends on a number of factors such as owner and patient circumstances, the extent of spread and the malignant characteristics of the tumour.

Take home message:

Early detection and treatment is crucial and prevent the need for invasive and costly procedures such as Radiation therapy or chemotherapy and it may even save your dog’s life.