My dog's tumor was benign, but now it's malignant. What happened?

The rate of growth does not necessarily correlate to malignancy - some benign tumors can appear suddenly (such as a histiocytoma) and some malignant tumors can grow slowly (such as a soft tissue sarcoma). I will say that I would agree that the masses in your picture look benign, but my eyes aren't microscopes and ultimately the pathologist will be able to determine what these masses are. Try not to worry too much over the next few days - you'll have an answer soon!

Thanks for using Petco Pet Education Center, formerly Petcoach! Possibilities include mast cell tumor, soft tissue sarcoma, plasmacytoma, carcinoma, something of a benign origin, among many others. It should be something similar or the same as the FNA. Ultimately, the biopsy is what actually provides the definitive diagnosis. Feel free to contact us back once the results are available and we can try to guide you going forward the best we can. Let's keep our fingers crossed that it is something benign. Good luck and have a great day!

Plasma cell tumors of the skin are almost always benign in the vast majority of cases. Predisposed breeds include Cocker Spaniels, West Highland White Terriers and perhaps Yorkshire Terriers, Boxers, German Shepherd Dogs and Airedale Terriers, with a median age of 9–10 years of age when the mass arises. Surgical excision with good margins is curative in the vast majority of cases. Recurrence occurs in only a minority of cases (<8% of cases). There are malignant forms and they carry a worse prognosis but they only occur in <4% of cutaneous tumors. I don't think you need to worry about any malignant forms of this at this point in time.

Thank you for submitting your question regarding Dylan. A procedure known as a fine needle aspirate is used to diagnose tumors just below the skin. A small sample of cells are collected from the mass and evaluated under the microscope. If this was not done when the mass was originally called a lipoma then then diagnosis could have been incorrect. If this procedure was performed then there are two things that could have happened. First, I have seen cancerous masses that have fat cells interspersed throughout them. So the sample collected could have only revealed fat cells, while there were mast cells present that did not show up on the slide. The other scenario is that the original mass was a lipoma and a mast cell tumor has grown over it in the past several years. I have seen this happen as well. I hope this information helps!

Thanks for using Petco Pet Education Center, formerly Petcoach! Overall, from what I'm reading and seeing, I have a low level of concern about Mukwa. This lesion does not look typical of a mast cell tumor (though that type of cancer does not always follow the "rules"). In general, non-cancerous things do not become cancerous with time - though there are exceptions. Occasional vomiting is not necessarily something I equate with Mast Cell Tumors, but does warrant a chat with your vet to see if it's something worth looking into. More concerning signs to me would be decreased appetite, weight loss, or lethargy. Best of luck to you and Mukwa!

I believe I was the vet who answered your previous question about Siu q! I remember the name of your dog :-) If it's a benign tumor, then it does not need to be removed unless it's affecting her movement in some way, it gets really big, or if it's irritating to her (she's biting at it, scratching at it). I hope this helps :-)

Thanks for using Petco Pet Education Center, formerly Petcoach! This could be a benign or malignant growth. Given the fact that it is growing quickly, a malignant tumor is more likely. This is often differentiated by a test called a fine needle aspirate (FNA) which is a pain free, inexpensive and easy procedure which in most cases will help reach a diagnosis. Sometimes a biopsy is needed for a definitive diagnosis. I recommend that you have her evaluated by your veterinarian for further assessment and treatment. I am really hoping for something benign. Good luck and have a good day!