Treating mast cell tumors MCT Cancer in the Dog Treendale Pet Medical Bunbury

Treating mast cell tumors MCT Cancer in the Dog Treendale Pet Medical Bunbury

Mast cells are very nasty cancers in dogs seen frequently on the skin. They have many varying forms. We strongly advise you have all skin lumps checked that you find on your dog or cat. Often they aren’t anything to worry about but you must have them checked by a veterinarian.

Mast Cell Tumors vary considerably in appearance however they are usually, round to oval, raised, pink to red, sometimes fleshy but sometimes merely a pink thickening of the skin. They sometimes don’t seem like much to worry about at all but they can be deadly.

Here is an example of a canine MCT

canine MCT

A good veterinarian will examine any unusual lesions for you and do a fine needle aspirate of the lump. The tumor cells can be seen in the cytology of the smear viewed under the microscope.

The mast cell cancer cells can also vary considerably depending on the grade of cancer. A feature of these cells is they contain lots of small granules of histamine. See the photo below. The large circle is the nucleus of the cell. The small purple dots are granules in the cytoplasm that contain histamine and also heparin.

Note the tiny purple granules in the cytoplasm of the cell. These are a feature of mast cell tumors.
If a diagnosis of canine MCT is made we will recommend staging the tumor with a view to wide margin surgical excision of the mass. We do surgery with curative intent in mind. The best chance of curing canine MCT is at the initial surgery with wide and deep surgical margins to make sure all of the tumor is removed with a healthy margin of normal tissue around it and below it.

Prior to aggressive curative intent surgery, it is important to stage the tumor. What does this mean exactly. Explained very simply, staging the tumor is an attempt to see whether it has spread already. Surgical removal is then important and the mass must be sent for histopathology for grading.

What is staging of canine mast cell tumors in the dog? Staging canine MCT in the dog is explained simply like this.

  • STAGE 1 is a single tumor that has not spread
  • STAGE 2 is a single tumor that has spread to the local lymph node
  • STAGE 3 is characterized by more than one skin tumor, or by a large tumor that is swollen and has invaded the deeper subcutaneous tissues.
  • STAGE 4 involves the presence of a tumor, with metastasis (spread) to other organs (typically the spleen, liver and lungs) or are present in high numbers in the blood

Once staging is done, we can determine whether surgery is going to be helpful. As mentioned previously, it is important to surgically remove these cancers with wide margins. The lesion is then sent for histopathology to confirm diagnosis and to grade the tumor. What is grading of canine mast cell tumors in the dog?

This is a simplified answer to help you understand what the different grades mean.

  • GRADE 1 is the best case scenario. These have not usually metastasized (spread). There is a 90% chance that proper curative intent surgery with wide margins will save your dog.
  • GRADE 2 are an intermediate grade of tumor. There is roughly a 50% chance that surgery will be curative but unfortunately about a 50% chance the tumor may have seeded or metastasized.
  • GRADE 3 is the really bad one. 90% of Grade 3 MCT’s will have already spread. Unfortunately there is only about a 10% change of a surgical cure. It is still important to remove the mass but follow up chemotherapy is recommended.

Explained in more scientific detail, a Grade 1 tumor shows well differentiated cells. They are contained and less likely to spread. Grade 2 MCT’s are less well differentiated and more likely to spread into adjacent cutaneous lymphatics and therfore find there way into other parts of the body. Grade 3 MCT’s are poorly differentiated or undifferentiated and are highly malignant, ie very likely to spread.

So if you see anything on your dog that looks like this (see below), you must go to the vet immediately and have it tested. Good outcomes can be achieved with diligent examination of your pet every month, accurate diagnosis, and good medical and surgical practices from your veterinarian. Canine MCT is a killer. You need to get any strange lumps tested by your vet.

mast cell tumors

A feature of mast cell tumors is that they sometimes “degranulate” when the veterinarian does a fine needle biopsy. Remember that these tumors contain histamine and also heparin. Histamine can cause inflammation like redness of the tumor and adjacent skin and the heparin can cause a loss of coagulation causing bleeding.

This canine skin tumor was investigated using a FNA needle biopsy. Note the redness of the tumor and the area of haemorrhage that continued to bleed profusely for several minutes. This feature of canine MCT can create problems during surgical removal. Just occasionally we can run into problems with a lack of clotting and profuse haemorrhage following excision of the cancer. This is a recognised complication. It can sometimes be challenging to control bleeding after removal of canine MCT’s.

mct cancer

This is what this tumor looked like cytologically under the microscope.

cell membrane

Note the cell membrane has ruptured and all the purple granules have escaped from the cells. This is called degranulation and causes redness, swelling and bleeding.

This is a crucial point. Owners often note that these tumors sometimes “swell up” but then go back down. The client becomes very worried when the tumor enlarged but then stops worrying when it goes back down so doesn’t go to the vet. If you notice a pink or fleshy lump on your dog that suddenly got bigger but then went back down, this is a feature of canine mast cell tumors in dogs. You must get it checked by your vet

purple nucleus

Here is another MCT. Note the large purple nucleus and purple granules.

What can I do if my dog has Grade 2 or Grade 3 canine mast cell tumors? Following surgical removal of the tumor chemotherapy is recommended.

What can I do if my dog has Grade 2 or Grade 3 canine mast cell tumors and I don’t want to do chemotherapy? You can palliate your dog with prednisolone. This may slow down the growth and spread of the cancer. It isn’t curative but may give you some extended time with your dog and improve the quality of life in the short term.

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