If you read part one, you remember I was all excited after a recent weekend meeting in New York City on the topic or oral malignant melanoma.
As discussed in my chapter in the Dog Cancer Survival Guide, oral melanoma is the most common tumor in the mouth of dogs, accounting for 30-40%. It is aggressive in the mouth and also highly metastatic. There are many treatment options for melanomas, and it continues to be a topic of interest for oncologists and Guardians.
Let’s pick up on some highlights from the VECOG meeting.
Topic 3: Melanoma Pathology
Dr. Mike Goldschmidt discussed the epidemiology and pathology of canine melanoma. The University of Pennsylvania has collected date from over 6200 dogs with melanoma. Based on this data, breeds at risk for oral MM include the Tibetan spaniel, Chow Chow, Gordon setter, Irish setter, Pekingese, Bloodhound, and Giant Schnauzer. Breeds over-represented as at risk for the digit form, according to UPenn were Rotties, Schnauzers and Scotties. Schnauzers were over- represented in all anatomic forms – oral, digit, skin and lip. Also, oral tumors were the majority (>50%) of melanomas.
This data is important, because we need to understand what dogs are at risk and how the tumor will behave, so we can diagnose these and treat these aggressive tumors.
Dr. Matti Kiupel is also a pathologist and traveled from Michigan State University to discuss diagnosis and prognosis. Melanomas are infamous for being hard to diagnose. It is a frustration of mine and is for most other vets. The biopsy can often be vague, indicating that there is a tumor, but which type is questionable – maybe melanoma, maybe connective tissue timor (sarcoma), or even a round cell tumor or a carcinoma. These tumors can quite difficult to diagnosis from biopsy, especially if the tumor lacks pigment.
Dr. Kiupel reviewed a great special stain “cocktail” that can be used to try to confirm the diagnosis in challenging cases. This was recently published by Dr Kiupel’s group and is something I have already used for my tough cases. We also reviewed features from the biopsy that have been shown to be predictive, such as nuclear atypia, mitotic index, and Ki-67. We also discussed that more than 1 parameter should be used to confirm diagnosis. This is one of the reasons we emphasize getting a second opinion on your dog’s biopsy — and it’s good to know about the melanoma stain cocktail, too.
Topic 4: Melanoma from a surgical oncologist’s perspective
Dr. Nick Bacon gave a great presentation on melanoma surgery. As he said, it’s not about bigger surgeries; we should be going for better results with less surgery.
We also talked about removing lymph nodes near the tumor. This is a murky issue, because we are getting better at finding metastasis earlier, and we might need to change how we deal with lymph nodes because of this.
Typically, for these tumors, a surgeon only removes enlarged regional lymph nodes, and/or those which show metastasis in an aspiration. We leave others intact, because, the thinking goes, they may provide a barrier to future metastasis. But it looks like this may no longer be the best way to handle regional lymph nodes.
If we only do an aspirate, or if we rely on how they feel to our touch, we risk leaving in a lymph node that is affected (false negative). Remember, you cannot tell for sure what you’re dealing with without a biopsy. And it turns out that lymph nodes are not very good at stopping the spread of these tumors, after all. We’re sometimes finding more metastasis than expected when we remove and biopsy regional lymph nodes.
So this means the statistics we’ve been relying on may be less accurate than we thought — because there may be metastasis where previously we would have thought there wasn’t. So, now that we’re getting better at finding metastasis earlier in these regional lymph nodes, maybe we should change our direction and remove regional lymph nodes, after all. That way we could start giving Guardians a clearer and more accurate prognosis. We would know more about the survival times, and what direction to head in with post-surgical treatments.
It’s often true that in medicine, the more we know, the more murky the terrain gets. We’re constantly clarifying everything. And as new techniques come along, old problems can be solved, but new ones can pop up. This discussion of whether to remove and biopsy regional lymph nodes will, I am sure, continue. And as we continue to clarify, we may start to routinely remove regional lymph nodes — even those that seem normal — for these tumors.
This is a challenge that I have already seen this my patients. For example, in my practice we routinely CT scan the lungs for staging, instead of X-rays. It’s hard to know if finding early lung metastasis (that would have been missed with X-rays) will worsen that dog’s prognosis. Most studies use X-rays for staging. I still think more accurate staging tests will help us help our patients, but this is relatively new territory and will definitely be an area of much research in the near future.
Staging and tests are useful to Guardians in terms of getting the most accurate prognosis. But remember, prognosis means “educated guess.” So what we talked about in this meeting — and what will continue to be discussed — is really us scientists trying to be better educated about these tumors. For you, the choices will still be hard.
There is an entire chapter dedicated to melanoma in the Dog Cancer Survival Guide if you need more information.
All my best,