When I bathed my old dog (10.5) a couple of weeks ago I noticed a puffy swelling between her 3/4 toes (hind leg). The vet put a needle into it & from what he saw said looked like mast cell tumour. It was operated on but due to where it was couldnt get it all so left dirty margins. Biopsy confirmed MCT.  We've got a few options to consider:
Remove the toe & hope that gets it all
Try radiotherapy (with or without amputation)
A drug has also been mentioned, Masivet, looking at the data sheet there can be, as with all drugs, side effects, which a younger dog may be able to shake off but an older dog?
Leave alone, wait and see.
There were no symptoms apart from the swelling which was hard to spot because of her fur. She is otherwise good & healthy for her age/breed.

Any experiences gratefully received.

How well is she in herself? Would she be able to cope with an operation to remove the toe? A friend of mine dog had her toe amputation for another reason and she's coped fine, however she is a lot younger..

What grade has the tumour been given? I think that would have a dependency on the possible answers to this.

My personal opinion in this would be if she is up to it remove the toe, do another biopsy and see, if all has been removed then brilliant, however if not then I would look again at the options open to you.

Hope all goes well for her xx

She's 100% in herself so you wouldn't know. The grading was difficult but 2 was given (it was explained but not very well) due to I think, where it was. I'll get another vet to explain in more detail when we go for a bandage change.  She is insured so that's one worry less!

In 2010 Winnie (then nearly 7) had surgery to remove 3 lumps. 1 turned out to be benign, another was grade 1 and the last was a grade 3 MCT (the worst it could be), so she had follow-up major surgery and they were able to get clear margins. This was followed by chemotherapy which she tolerated well, and now 18 months later she's still here and fit and healthy. If she hadn't had the major surgery and chemo the vet guessed she'd have 3-6 months, but with treatment probably 5 years+. As you can imagine I'm now paranoid about any lumps and bumps any of the dogs get. I hasten to add all these lumps were pretty innocent looking, and all slightly different, which is the problem with MCTs.

I'd recommend removing the toe to get clear margins, as she's fit and healthy otherwise, but I'd make sure of the grading first and the prognosis.

Removal of the tumour the vet needs to remove 3cm diameter  of the lump to be fully clear and depending on breed this could mean the entire foot. However im not sure what the option is otherwise. Have the lymph nodes been checked yet?

What i do know is my friends lab had a mct in the mouth which is apparantly rare place to get it, he recovered well after removal and has had no signs of anything nasty returning for 2 years now.