Mast Cell Tumors in Cats

Question: Dear Dr. Richards,

I hope you will be able to provide me with some words of wisdom as to the treatment of my own pet cat.

The cat is a 14 3/4 year old female who was losing weight. An ultrasound and needle biopsy showed a malignant mast cell tumor in the spleen. About a month ago she had a splenectomy and is recovering and eating well. There were no signs of metastasis and the liver looked okay to the surgeon. The tumor was 12 x 20 mm. Her blood work is normal.

My question is what is the optimum treatment at this time? Another veterinarian suggested prednisone would lengthen her life. The cat now weighs about 8 pounds and and seems to eating normally. We are currently giving her 5 mg prednisone daily, but I believe this dosage may be too small for any chemotherapeutic effect.

Thank you for your time, Alec

Answer: Alec-

Splenectomy alone provides pretty good survival times for cats with splenic mast cell tumors (around 14 months to 18 months based on averaging a couple of reports) as long as they haven't spread somewhere else. Since cats seem to get these tumors at older ages than dogs, on the average, the survival time has to be considered in light of the age of the patients at the time of diagnosis. I'm not sure what the estimated average survival time is for a healthy 14 year old cat but it probably isn't a lot longer than 2 to 4 years.

Chemotherapy is an option but the most common recommendation appears to be to use an H2 antihistamine blocker, like famotidine (Pepcid AC) post surgically. I think that this recommendation has to do with histamine release at the time of surgery but it may also be helpful as a longer term medication. In dogs, there seems to be a benefit from prednisone, in at least some cases, but for cats prednisone is not recommended as often. I'm not sure why, but it probably has to do with the fact that cats do well with surgery alone so it just seems less necessary. When prednisone is used in dogs it is usually used at 1mg/kg of body weight, so you are definitely in the therapeutic range giving 5mg to a slightly less than 4kg cat.

I honestly do not know how helpful it would be to consider additional chemotherapeutic agents (cytoxan, vinblastine, etc). If you wish to consider this option, it would be best to ask your vet to refer you to a veterinary oncologist who can probably provide more information on the success associated with using these agents and the expected complications of their use.

Mike Richards, DVM 2/25/2000

Mast Cell Tumor

Q: My cat had a bump behind her ear that eventually grew, and my vet removed it. I just got the biopsy results back, and it was a mass cell tumor. He told me that in dogs, there are levels to classify the severity of tumors, but there are no levels for cats. I never really got a clear answer of whether or not it is malignant, and I'm to talk to him again about treatment. He said he was concerned because of how extensive the tumor was. Do you have any additional information on mass cell tumors in cats? What is the survival rate, and can they be treated?

A: Holly- Most mast cell tumors in cats are solitary benign tumors but they can be malignant. In most cases simply removing the tumor is sufficient. If your vet is worried, it may be worth consulting with an oncologist to see if something like postoperative radiation therapy or chemotherapy may be helpful. The oncologists tend to have the most recent information on success rates, etc. when it comes to tumors and tumor treatments. Mike Richards, DVM

Mast cell tumors

Q: Our cat has mastocytoma, what is is and what should we do ? We have been offered steroid treatment by our vet, is this the best treatment? best wishes, mal

A: Mal- Mast cell tumors in cats are normally solitary and not very likely to be malignant. I am under the impression that the best thing to do is remove them. In dogs, they are usually malignant and it is necessary to remove them and to use radiation or chemotherapy (prednisone is used for chemotherapy of mast cell tumors) to prevent recurrence. I will try to remember to check on this when I get home since I am working from memory (I am away from my office this week).

Mike Richards, DVM

continued

Q: Thank you for your reply. Our vet is currently of the view that we should just leave the nodes alone while there are no other symptoms. She gave us 'pred 50mg' 2x per day, which I presume is what you said in your mail. She says we are to have weekly check ups from now on. If you have any more thoughts on anything we can do and what we can expect I would appreciate it, mal

A: mal- There are many times when we elect to take a "wait and see" approach, too. In most of those cases the lymph nodes eventually returned to a more normal size over time. Watch for other signs of illness, such as weight loss, vomiting, fever or pain. Report any of these things to your vet right away.

The odds are with you that the problem will resolve with time. Mike Richards, DVM