In defense of the incisional biopsy in veterinary oncology cases

After 15 years in practice, it is my distinct impression that convincing a pet owner to perform an incisional biopsy of a tumor is about the toughest sell in all of veterinary medicine. (OK, OK, maybe the notion of “strict cage rest” for orthopedic injuries is tougher, but still.) After all, it's difficult enough to convince owners to pay for histopathology at all after a tumor has been removed. Why on earth would they consider paying for it twice?

I think this point of view is a shame, because there are of a number of medically sound reasons for performing an incisional biopsy. All of these have been reviewed in textbooks or the veterinary literature and are likely well-known to most practicing veterinarians. Stuffy recommendations from medical textbooks, however, are unlikely to resonate with pet owners, so here I will speak plainly to the most important reason for performing an incisional biopsy. Namely, the incisional biopsy serves to manage the pet owner's expectation of the benefit that can be derived from attempts at definitive treatment for a cancer.

What cutting can (and can't) do

Managing client expectations is of critical importance when treating pets with cancer. This is because owners rarely understand what cancer treatments can and cannot do. I find this to be especially true where surgery is concerned. I have (unintentionally) brought many a pet owner to tears while describing what curative-intent cancer surgery actually entails. Their hopes of a quick, tidy snip-snip-stitch-stitch procedure to fix their pet's tumor quickly vanish when the discussion turns to the inconvenient details of fascial planes and surgical margins.

I do not say this callously-it brings me no more joy to make someone cry than it does any other conscientious practitioner. But I do take satisfaction from these moments in knowing that I have helped someone see the truth about their pet's cancer. And the truth is this: Attempting to surgically remove a tumor is sometimes a very bad idea.

The reason for this, of course, is that serious complications can arise from unconsidered attempts at surgical tumor removal. Hemorrhage, infection, dehiscence, and always, inexorably, the scourge of cancer recurrence should be at the forefront of the surgeon's mind when planning the resection of a tumor. Developing strategies to minimize the risk of these complications requires foreknowledge of the tumor's clinical biology-information often afforded by a well-procured incisional biopsy. This information notably includes tumor type and histopathologic grade, which are intimately associated with the treatment of choice as well as prognosis for most tumors.

Knowledge of tumor type, for example, may affect treatment decisions for cutaneous and subcutaneous round cell tumors, such as mast cell tumors, plasma cell tumors and histiocytic sarcomas. These tumors are often managed surgically but also respond well to chemotherapy or radiation therapy. Opting for these treatments over surgery may be wise if the surgeon believes the likelihood of complete excision is low or surgical complications high. Knowledge of tumor grade also may affect the decision to pursue surgery, as the likelihood of local recurrence for high-grade mast cell tumors (36%)¹ and soft-tissue sarcomas (up to 75%)² is significantly greater than that for their lower-grade counterparts (likely ≤10% for mast cell tumors1^,3 and approximately 10-30% for soft tissue sarcomas).^2,4

Low-grade tumors are thus often excellent candidates for surgical resection, whereas the choice for surgery must be made more carefully with high-grade tumors. This is doubly true because not only does tumor grade affect the likelihood of local recurrence, but it is also a powerful determinant of a patient's overall survival time, as high-grade tumors are significantly more likely to metastasize than low-grade tumors.

Forewarned is forearmed

Forearmed with this knowledge about the likely benefit (or harm) to be derived from surgical tumor removal, pet owners can make informed decisions about what course of treatment they wish to pursue. Knowledge of the potential complications associated with surgical removal may prompt owners to choose lower-risk options, such as palliative radiation therapy or chemotherapy. Knowledge of the prognosis for survival may prompt owners to forego definitive therapy altogether, opting instead for a hospice-style approach to their pet's care.

It may be tempting to view this pivot from a potentially curative approach to a purely palliative one as failure to deliver good patient care. It's not. Providing owners with the truth-however grim-about their pet's cancer using minimally invasive techniques, as opposed to stoking false hopes while potentially doing significant harm, is the essence of compassionate, thoughtful cancer medicine.

Veterinarians must bring this thoughtfulness to bear when recommending an incisional biopsy to a client and performing one on a patient. The procedure is, of course, not indicated for many tumors (see Figures 1 and 2).

Figure 1

Figure 1: Low-grade soft tissue sarcoma on the dorsal lumbar region of a dog. The tumor is relatively small, not adherent to underlying tissue, and located in an area where wide surgical excision is possible. Fine needle aspirate cytology was consistent with a mesenchymal tumor. Although incisional biopsy is not contraindicated, it is also perhaps unnecessary given the physical characteristics and anatomic location of the tumor. The tumor was cured by wide surgical excision. (All photos courtesy of Dr. Michael Childress)

Figure 2

Figure 2: Cutaneous mast cell tumor at the medial canthus of a dog (arrow). The tumor is small but located at an anatomic site where incisional biopsy is as technically challenging as definitive surgical excision. The tumor was diagnosed by fine-needle aspirate cytology. No biopsy was performed, and the owner opted to treat the dog with localized, superficial radiotherapy (strontium-90 plesiotherapy).

In tumors for which it is indicated (see Figures 3 and 4), the clinician must be cautious to avoid the two major complications of incisional biopsy: (1) obtainment of a nondiagnostic sample, and (2) seeding of cancer cells along the biopsy tract.

Figure 3

Figure 3: High-grade soft-tissue sarcoma in the dorsal interscapular region of a dog. The anatomic site of the tumor makes it potentially amenable to wide excision. However, the tumor is large and fixed to underlying tissues. The red discoloration and ulcerated surface suggest, respectively, induction of a localized inflammatory response and the presence of regions of hypoxia or necrosis within the tumor. Both of these characteristics are associated with aggressive malignancies. Unplanned excisional biopsy of a tumor with this appearance is likely to result in tumor recurrence or other surgical complications. In this case, the diagnosis was achieved by incisional biopsy, and the owner opted to treat the dog with palliative chemotherapy.

Figure 4

Figure 4: Squamous cell carcinoma of the rostral mandible in a dog. Veterinarians are often requested to surgically remove tumors such as this one for cosmetic reasons. However, pet owners must understand that local recurrence inevitably follows resection of such tumors without including a wide margin of surrounding bone. The broad-based appearance and imperceptible borders of this mass make it a poor candidate for excisional biopsy. Rather, imaging studies (either radiography or computed tomography to assess bony involvement) and incisional biopsy are indicated. This tumor was cured by partial rostral mandibulectomy.

To avoid the first of these, it is essential that the biopsy be of sufficient size and quality to allow the pathologist to render a useful interpretation. As such, the biopsy should be as large as is reasonable (the incision does have to be closed, after all) and consist of tissue that is not grossly hemorrhagic or necrotic. To avoid the second, the biopsy should be obtained in such a way that the entire biopsy tract can be excised if definitive surgery is pursued afterwards. Contamination of fascial planes around the tumor during an incisional biopsy can seed cancer cells at the tumor periphery, possibly increasing the risk of local recurrence after definitive surgical resection.

If pursued judiciously, incisional biopsy rarely results in these (or other) complications. Despite its safety, clients may still raise objections to the procedure. Some may claim that incisional biopsy increases the risk of cancer metastasis. It doesn't. Metastasis is, to an overwhelming degree, determined by the cancer's underlying biology. Most cancers that will metastasize have already done so by the time they are detected. Other clients may balk at the added expense. But the expense is a bargain compared to that paid financially and emotionally when a well-intentioned but ill-considered attempt at surgical excision goes awry.

A high-quality, properly collected biopsy is an absolute prerequisite to successful cancer therapy. It is my firm belief that when the true value of an incisional biopsy is properly explained, this “hard sell” quickly becomes a no-brainer, even to the most intransigent pet owners.

References

1. Donnelly L, Mullin C, Balko J, et al. Evaluation of histological grade and histologically tumour-free margins as predictors of local recurrence in completely excised canine mast cell tumours. Vet Comp Oncol 2015;13:70-76.
2. McSporran KD. Histologic grade predicts recurrence for marginally excised canine subcutaneous soft tissue sarcomas. Vet Pathol 2009;46:928-933.
3. Smith J, Kiupel M, Farrelly J, et al. Recurrence rates and clinical outcome for dogs with grade II mast cell tumours with a low AgNOR count and Ki67 index treated with surgery alone. Vet Comp Oncol 2017;15:36-45.
4. Bray JP, Polton GA, McSporran KD, et al. Canine soft tissue sarcoma managed in first opinion practice: Outcome in 350 cases. Vet Surg 2014;43:774-782.

Dr. Michael Childress is associate professor of comparative oncology at the Purdue College of Veterinary Medicine.