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

Five Common Mistakes with Cancer Surgery, and How To Avoid Them In Your Dog

Updated: September 23rd, 2019


These are the five most common mistakes with cancer surgery. Read on to find out how to save both time and money (yes, really).

There are five common mistakes with cancer surgery I see way too often in practice. Review this list to make sure that you are doing your best by your dog, and please see chapter 11 in our book to read more about surgery and how to prepare for it.

Mistake # 1: Watching and Waiting

Don’t: Watch the bump or lump. Do: get an aspirate or biopsy.

I’ve blogged about this before, but it deserves repeating. No one, not even a boarded oncologist like me, can look at a skin mass, or a mass in the spleen, liver, or lung on imaging, and tell you what it is. I may have an educated guess. But every lump and bump should be aspirated or biopsied so the cells can be looked at under the microscope. Even if your dog has had 10 lipomas before – like Smokey who belonged to my head nurse – the 11th may be malignant. In Smokey’s case, it was a low-grade soft tissue sarcoma (STS). (Click here to read more about Smokey’s story and why you shouldn’t watch and wait.)

If the aspirate is non-diagnostic — if it doesn’t tell you definitively whether cancer is present or not — then get a biopsy. We need to know what that bump is before it gets cut out. I know it’s tempting to just have your vet take the whole mass off, but you won’t necessarily be saving time or money. If the bump doesn’t get removed completely, for example, you might need to do a second surgery. That can lead often to a worse outcome for your dog. Biopsies help us plan surgeries — if the mass is malignant and the surgery is not properly planned, your dog will likely need a second surgery to get wider margins – that important normal rim of tissue around the cancer to prevent the cancer from coming back.

What’s my recommendation? If your dog has a skin mass that is 1 cm (yes, get a ruler and measure it), and it’s been there for a month, find out what it is;  I call this “see something, do something.”

Mistake #2: Removing a Bump or a Lump Without Knowing It’s Cancerous

Don’t:  Remove a mass without knowing what it is. Do: get an aspirate or biopsy BEFORE the surgery to remove the whole thing.

Please learn from the many patients I’ve seen over the years  in my practice. The story goes something like this: the dog has a skin mass that was just removed, without knowing what it was. The tumor was malignant, and now the bump is back, because the margins from the first surgery were dirty (aka incomplete) or narrow. Now the pet needs a second surgery, also called a scar revision, to widen up the margins to prevent local recurrence near the scar.

When a vet removes a mass to diagnose AND treat a mass (or a bump or lump), it’s called an excisional biopsy. Trust me, this is rarely the best first step in diagnosis for your dog. Excisional biopsy leads to incomplete margins, more treatment, more side effects to your dog, and more expense to you.

There are exceptions: excisional biopsy is okay when knowing the tumor type does not change surgery. For example, if a dog has a solitary splenic mass, the whole spleen should be removed whether it’s a benign hemangioma or malignant hemangiosarcoma. Another example is a tumor in the testicle. A castration is recommended regardless of the tumor type.

But for a skin or subcutaneous mass, the extent of surgery is changed by tumor type and sometimes by the grade of the tumor. If it’s a benign skin tumor, a marginal resection is fine, but for a STS like Smokey’s or a mast cell tumor, the first surgery should be wide. If it is in challenging location like lower on the leg or an oral tumor, maybe a boarded surgeon should do the first surgery. We might want a CT scan before the surgery to allow the surgeon to plan appropriately and get clean, wide margins the first time.

Remember: for many tumors, the first surgery is the best chance for cure.

To learn more about surgery and dog cancer, get a copy of this informative seminar!

Mistake #3: Declining a Biopsy

Don’t: Decline the biopsy. Do: Have your vet submit the tissue to the lab.

Every mass removed should be examined under the microscope at the lab. If your dog had 4 masses taken off, all should go to the lab –even if you or your vet thinks the masses “look” benign. Just this week, I saw Bella. She had two masses removed, but the vet only sent one to the lab. That one turned out to be malignant mast cell tumor (MCT). The other mass was not submitted. The MCT has narrow margins, so my surgeon had to do a scar revision. Was the other mass also a MCT? Maybe, maybe not. Fifteen to twenty percent of all dogs with mast cell tumors have multiple tumors — but we will never know at this point if Bella is one of them.

If it is important enough to remove, it is important enough to find out what it is – remember out vet eyes are not microscopes.

Mistake #4: Assuming Clean Margins Are Really Clean

Don’t: Assume clean surgical margins were clean.  Do: Ask how wide those margins were, and are they wide enough for this tumor type.

I often see dogs and cats months after a tumor was removed and then grew back. When I read the original biopsy report, it will often read: margins were clean. Good news, right? BUT when I read the microscopic decision, the measurement will say <1mm. For a malignant tumor, this is not considered clean!!

For many malignant tumors 2 to 3 cm are recommended. For soft tissue sarcomas (STS), tumors with incomplete — “dirty” — margins are ten times more likely to recur.

So, sadly, I am not surprised that these malignant tumors that were removed with narrow margins grew back.

I’m a little surprised how often this important detail is overlooked.  For a benign skin tumor like a sebaceous adenoma or a benign liver tumor, margins of a few millimeters are fine, but NOT for the malignant ones. So, remember, size matters! Ask how wide the margins were (get numbers) and ask if that is wide enough for this tumor type. If your vet isn’t sure, ask to see an oncologist.

For more, get a copy of the Dog Cancer Survival Guide

Mistake #5: Thinking a Specialist Costs More

Don’t: Be afraid to seek out a specialist for surgery. Do: Ask for a referral.

Boarded surgeons are more aggressive at surgery, in a good way. Studies show that for malignant tumors, patients often have better outcomes when the surgery is done by a specialist. Why? By removing more tissue, the first time, they are more likely to get those clean and WIDE margins and prevent the need for a second scar revision surgery. They are trained in advanced techniques, like flaps, which can help get margins. In the long run, this will save you money because you’re paying for one surgery, not two. Your dog will also undergo less treatment, have lower risks of side effects, and a better recovery.

Boarded surgeons are also often trained in proper biopsy and surgery techniques to avoid contamination and spread at the time of surgery.

Live longer, live well.

Dr. Sue


Discover the Full Spectrum Approach to Dog Cancer

Leave a Comment

  1. Christine on December 4, 2019 at 7:17 pm

    What is Dr. Sue’s advice on lumps that are less than 1cm and been there for more than 1 month? My vet says it’s too small to aspirate so he just wants to remove it without knowing what it is. I plan on getting a second opinion but also curious what your expert recommends. Thanks.

    • Dog Cancer Vet Team on December 5, 2019 at 6:47 am

      Hello Christine,

      Thanks for writing! As Dr. Sue writes in this article, if a lump is larger than 1cm OR has been there for over a month, to get it aspirated. She also writes in that article if your veterinarian won’t perform a fine needle aspirate/biopsy to find someone who will 🙂

      We hope this helps to clarify her recommendations 🙂

      • Christine on December 5, 2019 at 8:35 am

        Thank you for the quick response. If the lump is a suspected mast cell tumor, what are the chances that a FNA will cause degranulation and release histamine and heparin? I am worried that the procedure will cause uncontrollable bleeding and/or other systemic problems.

  2. Josephine Testa on September 24, 2019 at 11:50 am

    My holistic vet believe that by getting a aspiration it wakes the cancer. What do you think of that thought.
    She recommends just watching the lump and if it stays the same size leave it.

    What is your opinion on that?

  3. James Lynch on September 13, 2019 at 12:14 pm

    So the vet stuck a needle into my dogs lump and nothing seemed to come out in the needle. I saw him push the needle in twice pulling back on it twice to draw fluid. It looked like nothing came out. So he took a blood sample to check . Should I be concerned

  4. Crystal on June 6, 2019 at 7:30 am

    Thank you for the article. I took my 11 yo collie/greyhound mix in for biopsy for a tumor found in her chest. They said because of the placement, they couldn’t get a larger sample after the biopsy came back saying there were not enough cells to test. So the next step is to remove the mass from the lung. It is near the aorta, but they said there is plenty of room. Is surgery the next logical step despite we still don’t know what it is completely? Her heart and blood work all came back healthy. Would I be opening up more problems by having surgery?

  5. Barbara Zlotnik on December 12, 2018 at 4:36 pm

    Our italian greyhound has stage 2 mct. Biopsy showed not clean margins. Took him to UPenn for follow-up consult. They recommended 2nd surgery, but also said it was slow growing and at low chance of recurrence, with or without 2nd surgery. Still pondering which way to proceed, as dog is 10 yo.

  6. Lisa Pitts on July 30, 2018 at 10:51 am

    We have a 16yo male lab with a very large hard mass near his anus.( It doesn’t affect his ability to poop). I’m struggling with the decision to biopsy & remove the tumor, or just ignore it. My family is 4-1 , for removal….. …..i’m scared

  7. Tami Mcinnis on October 23, 2017 at 7:12 am

    sorry for your loss. I’m sure she will be in your heart forever and you will be in her spirit forever.

  8. Daycia Jensen on June 25, 2016 at 1:41 am

    Hi i have a 13year old shar pie . There was a lump growing on her belly close to wear hear back nipples were. The vet took xrays and toln me it was a tumor need to do a biospy they tried to remove as much of the tumor and then sent mass in for biopsy. It nas been over two weeks she is still drainimg to me that worrys me. Doctor said it should heal on it own in time. Is this true?second the tumor results came back it is carcinomatosis one was in the skin one in the memory gland.Since she has been on pain meds and antiboics she doesnt have a regular go potties. She tries to but little comes . Should i stop giving her the metronidazole and see if she goes?her bum is already inflamed trying to go and is sore . Im so besides my self. Please help give me advice. I hate seeing the dog that once had so much engery still at 13 just lay there and struggle

  9. Amy Kennedy on December 11, 2014 at 8:22 am

    we have a 9 year old golden who 2 years ago was given 1 month to live. She was diagnosed with Sqaumous cell carcinoma in her upper jaw, couldn’t let her suffer we did everything possible. Had it all removed Ignoring the $$$ signs she is now with us happier then ever.We listened to the Dr. and did everything right. Thank god she made it, can’t live without her!! Thanks to all the fabulous people dedicating their lives to our pets and all their illnesses!

    • Susan Kazara Harper on December 11, 2014 at 9:22 pm

      Thank you for sharing this; it’s important for everyone to know that there ARE good stories out there and there IS hope. Big cuddles to your girl.

    • jake purdy on August 11, 2017 at 9:14 pm

      This is such a great story. I just recently lost my cat to a battle with squamous cell carcinoma in the mouth. Her’s couldnt be removed because of its location. They gave her 3 to 4 months. I had insurance and had everything possible done to insure quality of life. She lived 9 months. I even fed her every meal and water by syringe for the last 3 months because it was only on her left side and didn’t hurt if I fed her liquid food I prepared for her on the right. She was the greatest gift and I will never have a connection to an pet like that ever again. I cried everyday from the day she was diagnosed til months after we put her to rest. She was the most loving and most loved creature. I cuddled her to sleep every night and my connection was so great that I swear we could communicate with each other just with our eyes and her expressions and the trust she had was undeniable. The oncologist said I was one of the best most caring owners she’s met. I only say that out of pride. Hearing your story brings tears to my eyes as I wish I had the option to remove the tumor. But because of her we recently got a new cat. Same Tuxedo breed (because of the joy Rajah brought to us) and she is just as cuddly and loving as Rajah. She is a gift from her. I really do believe that. Thanks for sharing. It brought back alot of great memories.

  10. Cat on October 18, 2014 at 11:39 am

    My 7.5 year old mixed breed 70lb dog has a large hemangioma on her upper outer rear gum- vet said it was a high grade aggressive type tumor. 5 weeks after removal it was back- big with black necrotic edge. Had it removed a second time… Would prednisone help slow the re growth? My vet says no but I would think it would help

  11. Michelle P on November 19, 2013 at 9:07 am

    Hi, I have an English bulldog/boxer mix who is 8 years old. About a year & a half ago she developed a large lump on her front leg which grew to be about the size of a baseball or fist. We had it removed this past April & by August it was back but now it has spread down her leg & is even bigger. She constantly limps & has a decreased appetite. I took her to the vet with a temperature of 104.5 but nothing was done. I’m starting to get very concerned with the size of the tumor, her limping & her lack of energy. Help…..what could this be????

    • Susan Kazara Harper on November 19, 2013 at 2:22 pm

      Hello Michelle, I know this is very worrying. You need a diagnosis, and because your vet has already removed a lump this year, it’s no good going through list of what it might be. Your vet should know. I recommend you call your vet practice and first ask what the diagnosis was of the lump removed in April. There should have been a biopsy done, and the details will be in your record. You mentioned the word tumor, which usually indicates that a lump is cancerous, but not always. Get the facts. Have you taken your dog to get this newer lump examined? If she is limping, even if the lump is not cancerous, it’s presence could impede on her muscles or the blood supply in the leg, and that’s not good. It’s important to get it checked out. A fever of over 104 could indicate an infection or something else going on, but really, only your vet can diagnose that. You have several symptoms; the lump, limping, fever and decreased appetite which may all be related. Please let your vet examine your dog and be very clear about what you are told. With a diagnosis your vet can then advise a treatment plan and you can move ahead to make her more comfortable. Good luck!

      • Michelle P on November 19, 2013 at 3:01 pm

        The reason I called it a tumor is because our vet said it was a tumor. She felt it was localized & didn’t think it needed a biopsy but stated she would store it in formaldehyde so if it was to grow back we could send it off. We went back a few weeks ago & I asked for it to be sent off but she can’t find it. When I questioned her about the lump coming back she just brushed it off & said we could just leave it or keep removing it so we are going to a new vet for a second opinion.

        • Susan Kazara Harper on November 20, 2013 at 3:11 am

          Hi Michelle, That makes sense and it sounds like you’ll be happier with a second opinion. You cannot move forward to help your girl without knowing what you’re dealing with, and you truly need a biopsy for that. Equally, keep in mind my earlier comments about if it’s just a fatty lump it may be in an area that even that could cause problems. Please don’t worry too much until you get to the next vet. I hope you can get an appt soon with a vet you like, to relieve some of the stress of not knowing. Good luck !

  12. Michelle Buenzli on November 7, 2013 at 10:22 am

    Tucker just had his surgery (by a boarded surgeon) last week to remove the new mast cell tumor. He wasn’t able to get clean margins in one area and microscopic cells remain. The oncologist is pleased by the fast healing of the incision though. In two weeks we will have a discussion on how to treat for the remaining cancer. In the mean time it’s benadryl, pepcid and dexamethasone.

  13. Michelle Buenzli on October 17, 2013 at 7:58 am

    Well, we made several of these mistakes with our Cairn, Tucker and I wish I’d had this information then! The aspirate didn’t give a diagnosis but we asked our everyday vet to remove it. They said they “thought” the margins were clean. We did have it biopsied and learned it was a mast cell tumor. Now 3 years later we are going through chemo with an oncologist and facing another surgery to remove a recurrence in nearly the same place.

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