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Featuring Demian Dressler, DVM and Sue Ettinger, DVM, Dip. ACVIM (Oncology), authors of The Dog Cancer Survival Guide

When to Avoid Chemo for Canine Mast Cell Tumors?

Updated: June 19th, 2019

There has been much online talk these days about dogs with mast cell tumors (read, Palladia) which are the most common canine cancer.

So I thought I’d just add some fuel to the fire and give my readers some overall guidelines about mast cell tumors and chemotherapy.

As many already know, these cancers come in different grades (1, 2 and 3).  Grade 1 are almost always benign, grade 2 are intermediate (some benign and some malignant) and grade 3 are universally malignant.

Your vet will give you the grade following receipt of the biopsy report, which is completed by a path lab after submission of tissue from the tumor.

Wide excision (removal of a large swath of normal-appearing tissue around the tumor) cures many mast cell tumors.  Pretty much all grade 1, and about 90% or so of grade 2 mast cell tumors are gone permanently after wide excision.  Grade 3 mast cell tumors are candidates for chemo and possibly radiation and more as they will often come back and spread even after surgery.

The tricky guys are those grade 2 mast cell tumors.  Since some behave like benign tumors and some like real cancers, what are we supposed to do?

Well, the key is in getting more information about your dog’s individual tumor. There are a couple of bits of information that are valuable that can help you predict the behavior of your dog’s grade 2 mast cell tumor.

The single most important one is called the  mitotic index.  This is the number of cells that are actually dividing seen by the pathologist under the microscope.

The magical cut off is somewhere around 5.  This means that if the tumor has a mitotic index of less than 5, it usually will behave less aggressively and in my opinion do not require surgery, as long as you have clean margins on the removed tumor.

More than 5?  We need to now consider hitting these guys with the full spectrum approach (diet, supplements, chemo, and other strategies discussed in The Dog Cancer Survival Guide).

You may read about other markers (kit, AgNORs, Ki67) but these are much less useful than mitotic index.  If the mitotic index is around 5 though,  consider these other markers for more data.

By the way, not all vets may know about this stuff, so remember to be your dogs primary health care advocate and speak up!  You vet is the one who has to order this testing of the biopsy specimen from your dog.

The squeaky wheel gets the oil!

Best to all,

Dr D

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  1. marge on November 10, 2018 at 6:08 am

    My 7 year old Jack Russel Beagle mix had an 8 cm X 2 cm subcutaneous mast cell tumor incompletely removed from his left rear leg 9 weeks ago by his regular vet and sent to pathology. Biopsy returned with the following: Mast Celll Tumor and –
    (1) “this neoplasm is closely excised with minimal clean surgical margins. Neoplastic cells extend 4 10 HPF; yes/no): No
    Multinucleated c. (yes/no): No
    Infiltrated patern (yes/no): No
    Two-tier grading (low/high): Low
    Surgical margins: <1.0 mm
    Angiolymphatic invasion: None
    Six weeks after tumor removal Rusty had CCL tear of same location as tumor and requires CCL repair that regular vet does not want to repair for fear of spreading remaining tumor. Question is whether "scar revision" surgery is needed at time of the CCL repair with "Extracapsular Stabilization", so as not to spread the remaining cancer cells, as recommended by one out-of-town surgeon who will be taking his board exams. Or should we go with a local board certified surgeon who recommends CCL repair using TTA procedure but without scar revision, because as explained, the TTA incision is under the leg and not above the leg where the tumor was removed, so there would be no access to the original scar tissue to do the scar revision surgery. He does not feel scar revision surgery is necessary or helpful but that radiation would be better. However radiation is only available at a distant location from us, Cornell U. in Ithaca, NY. Besides the question of the need for scar revision surgery, is the question of which procedure is better for the CCL repair, considering possible future complications with cancer in this leg? By the way, before tumor removal, a needle aspirate in three locations of the tumor showed only fat cells under vet's microscope, it was not sent to pathology and tumor was initially believed to be a lipoma prior to removal. Also, ultrasound guided needle aspirate of local lymph node sent to pathology and abdominal ultrasound, both at 8 weeks after tumor removal, were normal. We are confused and Rusty's condition is deteriorating in the meantime, as we try to get answers that are difficult to find.

  2. patsi on October 25, 2017 at 5:42 am

    I had a 6 year old toy fox terrier who had a mast cell tumor,used neoplasene to remove,along with zantac and benedrly. It was systemic,do had pop ups,which I removed for about 6 years,she had good quality of life . The tumor was diagnosed as cancerous by fine needle biopsy, although time consuming for me,it was a good treatment. I used tramadol during treatment,and here’s the truth. The neoplasene literally DUG the tumor out,and I carefully covered wide margins because these tumor are much larger underneath than what is visible on top,and made sure to let the tumor DROP of,no tugging,because you cannot leave any part of the tumor behind. I have kept several of these tumors,to me,the whole process was a miracle.

  3. Willoughby on October 26, 2014 at 2:25 pm

    My 50 pound husky just turned 13 a couple of days ago 10/23/2014. She is an age-defying, SUPER spunky and active girl. In September, she had a 3 cm x 4 cm MCT removed from her ear. An innocuous looking skin tag had been on the edge of her ear for six months or more, and then suddenly flared up in July into an ulcerated mass. It settled back down…then flared again and got bigger in a matter of a couple of weeks, and started heading inward toward her ear canal. After surgery (9/11/14), pathology deemed it a Grade 3 MCT. Ugh. I had ultrasound and liver and spleen aspirates done. No mast cells were evident…Back at the surgery site, the surgeon did not go at the tumor very aggressively, and while I expected that her whole ear was going to be removed, he just did a partial external ear canal ablation, leaving the pinna in tact. Pathology said clean margins were only 1 mm. I was very worried about it, but a second surgeon at the oncology center wanted to do a second surgery, with total ear canal ablation and a middle price estimate of $7000. I had just spent nearly $4000 for the last incomplete surgery and diagnostics AND I was just laid off my job. Palladia was also recommended. I had so many reservations about putting her through the complications of medication and another, really aggressive surgery, that I decided I would not go that route, and I would stick with supplements and diet. She has been on an all organic, home cooked diet with K9 Immunity Plus for more than two years (since having a 5.5 pound Hepatocellular Carcinoma removed from her liver two years ago (9/23/12). Along the way I have added probiotics, CoQ10, Curcumin, IP6/Inositol supplements–I have not used Apocaps, because of liver concerns–(There was a small mass on her liver evident in the ultrasound–aspirates suggest it is a recurrence of the Hepatocellular Carcinoma)…But then today, I noticed a bit of pink skin where her fur is just growing back in on the tragus of her ear. I found a marble sized growth there that I can tell you was not there two days ago, as I have been vigilantly checking the surgical site for signs of recurrence. There had been a very small bump on the tragus at the time of surgery…about 2 mm…which was removed and biopsied. No mast cells were found…but now…there is this alarmingly sudden and significant bump. I wish I knew what direction to go now. I will have this thing biopsied, but it seems most likely it is a recurrence of the MCT. I wonder what role that biopsy might have played in creating this new tumor. Mast cells turn up at the site of trauma as part of the normal immune system response….I wonder if some of those cancerous mast cells responded to the biopsied site and took up residence there. SO bummed, and seem to be stuck with the standard recommended protocol when seeking advice…Would LOVE to have input from Dr. D and/or Dr. Sue. I do have the guide, and have been referencing it these last two years…

    (She is also on Denamarin for liver support…and she has a slow growing mass in her lungs…discovered on radiographs at the time of her HCC removal…was 2 cm in diameter two years ago…now is at about 4 cm in diameter…could be a granuloma or a slow growing cancer…either way, she has never had any symptoms related to it…)

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