Oct 10 2017

Mast Cell Tumors – Case of the Week from Dr. John Glauser

dog laying on beach under blue sky

Our patient this week is a middle-aged mixed breed dog.  He developed a lump on the end of his docked tail that grew over several weeks.  He was beginning to show signs of discomfort with the lump and was licking at the area.  He felt otherwise fine.

Whenever new masses are found on or under a pet’s skin, I have a similar conversation with the owners – that is, as veterinarians, we cannot tell with certainty whether a mass is serious (malignant) or not (benign) just by look and feel.  In certain situations, a mass can have a characteristic appearance or feel and a veterinarian may feel comfortable identifying it as benign without further tests.  In this case, the mass was under the skin, and somewhat firm.  Given this, and the fact it was growing and causing discomfort, additional diagnostic tests were pursued.

A common first step test in diagnosing a mass is a cytology test.  To perform this test, a veterinarian must collect cells from the mass using a needle.  A needle is inserted into the mass and suction is applied with a syringe.  The material collected is then sprayed onto a slide and sent to a cytologist for identification.  A cytologist is a veterinarian with special training in identifying cells under a microscope.

After performing this test, a diagnosis of a mast cell tumor was returned from the lab.

Mast cell tumors are a common type of skin cancer found in dogs.  These tumors can be found on or under the skin and in some cases spread to the lymph nodes or organs like the liver or spleen.

To treat mast cell tumors, the tumor must be removed surgically.  Cells from mast cell tumors often extend beyond the visible mass, so wide margins of normal-appearing tissue around the tumor must also be removed to prevent the tumor from returning.

After reaching this diagnosis, this patient’s astute owner thoroughly examined his entire body and found another small lump near his hip.  This was tested and also found to be a mast cell tumor.

Both tumors were removed surgically.  To remove enough normal tissue around the tumor on the tail, the tail itself was shortened.

The tumors were sent to the lab for microscopic examination.  This test confirmed that each tumor was removed completely.

We will need to continue monitoring this brave boy for more tumors in the future, but for now we are happy to say he is cancer-free!

This is a great reminder of the importance of checking your pet regularly for lumps and bumps.  If you notice any new or changing lumps, be sure to have them checked by your veterinarian.

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