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Why Clean Margins are Crucial in Feline Oral SCC

A case study.


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My September column [“Early detection is key with oral cancer”] briefly touched on feline oral squamous cell carcinoma (SCC), but the topic deserves more discussion as a stand-alone column.

The diagnosis of oral squamous cell carcinoma in cats is even more dreaded than the diagnosis of oral malignant melanoma in dogs, and rightly so. Squamous cell carcinoma is locally invasive and rapidly growing in cats, and it is often difficult to obtain clean surgical margins by the time the tumor is detected in cats.

Promising Case 

The date was Dec. 16, 2015. Jennifer Kim, our medical oncologist at NorthStar Vets, came to me with excitement on her face. She had just seen a feline SCC patient that might be a candidate for surgery.

I, too, was excited when I looked in Randy’s mouth. The 14-year-old domestic shorthair cat was in otherwise good health but had histologically confirmed oral SCC of the left mandible, from the symphysis and extending caudally along the gingiva of the left mandible (Figure 1). 

Figure 1: Randy's left mandibular SCC. The mass was palpable at the level of the symphysis and extended along the caudolingual and buccal surfaces of the mandible to the level of the ramus.

John Lewis, VMD, FAVD, Dipl. AVDC

Figure 1: Randy's left mandibular SCC. The mass was palpable at the level of the symphysis and extended along the caudolingual and buccal surfaces of the mandible to the level of the ramus.

Our excitement stemmed from the fact that most cats presenting with oral SCC are too far advanced for us to even consider surgery. In Randy’s case, it seemed to be a possibility. Of the many cats with oral SCC that I see each year, only one or two are candidates for curative-intent radical surgery that may allow for clean margins on the tumor.

If clean margins are not obtained, the tumor will typically grow back very quickly. Putting a cat through a major recuperation for a short gain in survival time is not usually worthwhile.

Clear Objective 

I try to obtain at least a 1-centimeter margin around feline SCC in all dimensions, including skin. Some texts describe the hemimandibulectomy technique as incising the mucosa on the buccal and lingual sides of the mandible, peeling the skin away like a glove, removing the affected mandible and closing up the remaining mucosa. This is not a reliable method of getting margins in the ventral, lingual and lateral directions.

When I first started doing these surgeries almost 20 years ago, I did not consider the importance of removing skin when taking margins. Back then I was concerned with how I was going to close the surgical site if I removed so much skin. However, we are not attempting these types of surgeries with the intent of obtaining dirty margins.

Therefore, saving additional skin to allow for closure of a site with dirty margins should not be the goal of a curative-intent surgery. Creative skin flaps may allow for both goals of obtaining clean margins and being able to close the site primarily.

Similarly, even if the tumor does not cross the symphysis, removal of a portion of the rostral contralateral mandible is often necessary to get 1- centimeter margins in the medial direction. This was true in Randy’s case (Figure 2). 

Figure 2: The preoperative dental radiograph of the mandibles. The left mandible shows significant lysis, which extends beyond the symphysis.

John Lewis, VMD,  FAVD, Dipl. AVDC 

Figure 2: The preoperative dental radiograph of the mandibles. The left mandible shows significant lysis, which extends beyond the symphysis. 

First Steps 

Dr. Kim did a thorough workup before considering surgery. Distant metastasis is possible with feline oral SCC, and a recent study suggests that advanced cases have a higher rate of metastasis to regional lymph nodes than previously reported. Staging procedures for Randy included abdominal ultrasound, thoracic radiographs, head and neck CT to assess the tumor and deeper lymph nodes in the neck, and aspirate of mandibular lymph nodes. Luckily, all tests looked promising; there was no evidence of metastasis.

After removing the entire left mandible, the rostral right mandible at the level of the fourth premolar, and the intermandibular musculature and skin (Figure 3), the specimen was submitted for histopathology to confirm the previous diagnosis and to evaluate margins. The remaining molar of the right mandible was extracted to prevent palatal trauma after mandibular drift (Figure 4). 

Figure 3: En bloc removal of the entire left mandible, rostral right mandible, inter-mandibular muscle, and skin. 3-A is the dorsal view and 3-B is the left lateral view.

John Lewis, VMD,  FAVD, Dipl. AVDC 

Figure 3: En bloc removal of the entire left mandible, rostral right mandible, inter-mandibular muscle, and skin. 3-A is the dorsal view and 3-B is the left lateral view. 

The most challenging area to obtain margins was in the area caudolingual to the left mandibular ramus due to the proximity of the tongue’s blood supply and nerve supply. Unfortunately, evaluation of margins by the pathologist showed cancer cells at the left caudolingual margin.

Figure 4: A radiograph of the remaining portion of the right mandible. The remaining mandibular first molar was preemptively removed to prevent the sharp cusps from causing palatal trauma since mandibular drift was likely. Six months after the initial surgery, the right maxillary fourth premolar was extracted due to a pyogenic granuloma that occurred lateral to the caudal right mandible.

John Lewis, VMD,  FAVD, Dipl. AVDC 

Figure 4: A radiograph of the remaining portion of the right mandible. The remaining mandibular first molar was preemptively removed to prevent the sharp cusps from causing palatal trauma since mandibular drift was likely. Six months after the initial surgery, the right maxillary fourth premolar was extracted due to a pyogenic granuloma that occurred lateral to the caudal right mandible. 

Post-Surgery 

After Randy healed from the surgery, he returned to Kim for discussion of further treatment. Since the margins returned as unclean, the option of radiation therapy was discussed. The owner opted to pursue chemotherapy instead. Kim began toceranib (Palladia) therapy.

With the combination of surgery and chemotherapy, Randy has been cancer-free since December 2015. Historically, survival times have been poor with feline oral SCC. Of all of the papers in the literature, one study by Marconato, et al. has shown the most promise, which combined a multimodal approach to therapy including surgery, radiation and chemotherapy.

One big consideration is long-term function. One centimeter does not sound like a lot of tissue, but in a cat with an already large tumor, such margins in all dimensions can represent a huge loss of hard and soft tissue. This loss of jaw and surrounding soft-tissue structures can result in significant functional challenges for the feline patient, whereas a similar mandibulectomy in the canine patient will often be well-tolerated.

A retrospective study that looked at feline mandibulectomies found that 12 percent of cats never regained the ability to eat or drink again on their own during the follow-up period.

Randy needed an esophagostomy tube for six months before he began eating and drinking on his own, albeit sloppily. Randy required an extra surgery to extract the right maxillary fourth premolar tooth that was contacting alveolar mucosa of the right mandible and causing discomfort.

What can be done for the 12 percent that don’t eat and drink on their own? A permanent PEG feeding tube is one option. Only time will tell, but reconstructive locking plate technology coupled to recombinant bone morphogenetic protein eventually may provide a return to function for these cats, similar to what has been described in dogs.

References

  1. Soltero-Rivera MM, Krick EL, Reiter AM, Brown DC, Lewis JR. “Prevalence of Regional and Distant Metastasis in Cats With Advanced Oral Squamous Cell Carcinoma: 49 cases (2005-2011)” J Feline Med Surg. 2014 Feb; 16(2):164-9.
  2. Bilgic O, Duda L, Sánchez MD, Lewis JR. “Feline Oral Squamous Cell Carcinoma: Clinical Manifestations and Literature Review” J Vet Dent 2015; 32(1):30-40.
  3. 3. Arzi B, Cissell DD, Pollard RE, Verstraete FJ. “Regenerative Approach to Bilateral Rostral Mandibular Reconstruction in a Case Series of Dogs” Front Vet Sci. 2015 Mar 30; 2:4.

Dr. John Lewis practices veterinary dentistry and oral surgery at NorthStar Vets in Robbins-ville, N.J. Columnists’ opinions do not necessarily reflect those of Veterinary Practice News. 

Originally published in the November 2016 issue of Veterinary Practice News. Did you enjoy this article? Then subscribe today! 

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