The oncologist’s thoughts on what to do after the aspirate confirms mast cell tumor?

In my recent blog, we discussed the aspirate that confirmed the diagnosis of mast cell tumor (MCT.)

Now there is a decision to make, should you have your dog staged to make sure the MCT has not spread, or should you proceed to surgery to remove the tumor and find out the grade?

Remember what I said in this MCT post, this is not a one-size-fits-all tumor, meaning there is not a checklist or single protocol for all dogs. MCT is a complicated cancer.

Some Guardians choose to stage the cancer without knowing the grade, because if it has spread they might not go through with surgery and may just do chemotherapy, or no therapy. Other Guardians want to remove the tumor, get the grade information, and then proceed with staging tests.

Why go to surgery?

If I have a dog with his first MCT and there is only one MCT, going to surgery is typically the next step. If possible, the goal of surgery is to remove the entire visible tumor along with a wide (usually 2 to 3 cm on all sides and a layer of tissue below) margin of surrounding normal tissue. The surgical margin must be confirmed clean with the pathologist’s report. The surgical biopsy also provides the grade. Grade is one of the most important prognostic (or predictive) factors for MCT. We will discuss that in the next blog.

Location location location!

Who should do surgery? If the tumor is large or in a region where getting clean margins will be challenging, I urge you to consider seeing a board-certified surgeon. A good example is a MCT on a leg – there’s just not a lot of tissue on these areas, especially the further down the leg towards the paw.

There is evidence that board-certified surgeons are more aggressive in their approach – in a good way; they typically remove more tissue, which results in cleaner margins and fewer cancer recurrences.

Wide excision — which means a big incision or cut — is the best way to achieve local tumor control (prevent cancer from recurring).  Surgeons actually measure around the tumor and mark the measurements on the skin before making incisions at surgery.

If the margins are not clean, I am likely to recommend a 2^nd “scar revision” surgery. Which means the surgeon will have to go back and “revise” the scar — make it wider, basically, to get the tumor out completely. This is one reason I urge you to see a board-certified surgeon first, because your dog may require fewer surgeries. The first surgery is the best time to remove the entire tumor.

What if more than one MCT?

If there is more than one tumor, it is recommended to biopsy each one, because each separate tumor could be of a different grade and need a different course of treatment. If there are many tumors – more than four or five – I will often biopsy the two largest or the ones which have grown most quickly, depending upon the specific case, the location and size of the tumors, and my own discernment.

Do I stage prior to surgery and knowing grade? What does staging include?

It is always reasonable to look for spread prior to surgery. However, if your dog has a single Grade I tumor, further staging before surgery is probably not necessary.

But in all other cases – two or more tumors of any grade, a Grade II or III tumor, a recurrent MCT tumor, or lymph node metastasis – further staging is necessary before deciding upon a course of treatment.

If you did surgery 1^st and the biopsy reported a Grade II or III MCT, I will recommend staging after surgery.

Staging should include at a minimum an aspirate of lymph nodes in the region of the tumor or tumors (even if they are of normal size) and an abdominal ultrasound to check for internal metastasis. A bone marrow aspirate may also be needed.

Why an abdominal ultrasound? In addition to spreading to the draining lymph nodes, MCT tends to spread to the liver, spleen, and sometimes internal lymph nodes; an abdominal ultrasound will reveal suspicious lesions or enlarged, infiltrated organs. If these are found, it does not necessarily mean that there is metastasis; the organs should be aspirated to confirm the situation. In most dogs, aspirates are done using ultrasound-guidance and can be done without sedation.

There is still some controversy about whether normal liver and spleen should be aspirated. But a recent study (Stefanello 2009), showed that normal-appearing organs can still be infiltrated with MCT, and dogs with aspirates that confirmed this sadly lived much shorter. So it is important to know that if the liver and spleen are normal on the ultrasound, this may be a false negative. While the procedure is safe, quick, and harmless in most cases, it is important to go through the pros and cons with your oncologist.

Next blog will be about the biopsy report, grade, and mitotic index. In the meantime, remember there is a lot more information on MCT, including staging tests, in the Guide.