EMMA

Emma, a 10 year-old spayed female Black Labrador Retriever, developed a mass on the inside of her left upper lip.  The mass was first noted by her referring veterinarian on a routine examination.  Emma’s veterinarian took a needle sample of the mass and diagnosed a mast cell tumor.  The area around the mass swelled significantly after aspiration.  Emma was referred to Dr. Gustafson, our oncologist, who discussed options for treatment of mast cell tumors.

Cutaneous (skin) mast cell tumors are the most common skin tumor found in dogs.  They occur most commonly in older (mean age 9 years-old), mixed breed dogs, boxers, Boston terriers, Labrador Retrievers, beagles and schnauzers.  Mast cells are found in many tissues in the body and play a role in inflammatory and allergic reactions. 

Mast cells contain histamine which is a substance involved in allergic and inflammatory reactions.  It causes swelling and calls other inflammatory cells to the area.  For this reason, mast cell tumors will sometimes change size rapidly, growing and sometimes then shrinking back to their original size, especially after manipulation.  This occurs because irritation of the abnormal mast cell tumor cells can cause them to release histamine, which causes swelling and inflammation of the tissue around the mass.  This is why Emma’s tumor and her lip swelled so significantly after the aspiration.

There are three grades of mast cell tumors; grade 1, 2 and 3.  All mast cell tumors are very locally invasive, which means they send finger-like projections of microscopic tumor cells into the surrounding normal-appearing tissues, as shown in the drawing below

Grade 1 mast cell tumors, while locally invasive, do not tend to spread (metastasize) to other areas of the body and therefore can often be cured with complete removal.  Grade 3 mast cell tumors, in addition to being very locally invasive, also have a much higher rate of spread (metastasis) to other parts of the body.  Grade 3 mast cell tumors are therefore harder to treat, requiring not only removal of the original mass but treatment aimed at killing any tumor cells that have spread to other parts of the body.  Grade 2 mast cell tumors are very locally invasive and have a moderate risk of metastasis.  When mast cell tumors metastasize they most commonly spread to lymph nodes, the liver or the spleen.  Emma’s veterinarian had performed chest x-rays and an ultrasound of Emma’s abdomen and did not find any evidence of metastasis.

If possible, the best treatment for a mast cell tumor is complete surgical removal of the tumor and any surrounding microscopic tumor cells.  If complete removal is not possible, radiation therapy can be helpful in shrinking mast cell tumors before surgery or killing any remaining tumor cells after surgery.  Chemotherapy can also be used to attack microscopic tumor cells and is mostly used to kill cells that have spread (metastasized) to other areas of the body.

Emma’s lip was initially very swollen and the mass was too big to remove surgically.  Therefore, Dr. Gustafson began treating Emma with steroids and chemotherapy aimed at shrinking the tumor and associated swelling.  The swelling gradually subsided and the size of Emma’s lip mass shrank to the point that it could be removed surgically. 

Since mast cell tumors are very locally invasive, sending tentacles of microscopic tumor cells into the surrounding tissue, we need to remove 2-3cm of what looks like normal tissue around the mass to have the best chance of removing all of the tumor plus any surrounding microscopic tumor cells.  Emma’s palpable mass was now small enough to remove, however, only 0.5-1cm of tissue could be removed around some areas of the mass making it very unlikely that we would be able to remove all of the microscopic tumor cells around the mass.  For this reason, the plan was to remove the tumor and as large a margin of surrounding tissue as possible with the expectation that Emma would need radiation therapy of the area after surgery to kill any remaining microscopic tumor cells.

The mass on Emma’s lip was surgically removed, leaving an approximately 5cm wide rectangular defect in her lip similar to the one shown in the drawing below.