Page 188 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

CHAPTER 10 Surgical Oncology 167

TABLE 10.1 Classification and Resection of Wound
Margins
VetBooks.ir Type Plane of Dissection Result
Intracapsular
Tumor removed piecemeal or
Residual macro-
curetted, “debulking” scopic disease
Marginal Tumor removed on or adjacent Usually leaves
to the tumor pseudocapsule, microscopic
“shelled out” disease
Wide Tumor removed with margins of Possible skip
normal tissue lateral and deep lesions
to the tumor; tumor capsule is
not compromised
Radical Tumor removed with an entire No local residual
compartment or structure cancer
(e.g., amputation)
• Fig. 10.2 Computed tomography of a dog with suspected multilobu-
lar osteochondrosarcoma of the inferior orbit is used to provide three-
dimensional reconstructed images. This enables the surgeon to determine
the size and extent of the tumor and to plan the surgical margins and
approach accurately. Computed tomography is preferred for imaging of meaningful for tumors with a well-defined venous supply,
bone and intrathoracic masses. (From Johnston SA, Tobias KM: Veterinary
surgery: small animal, ed 2, St Louis, 2018, Elsevier.) such as splenic and lung tumors. Small numbers of can-
cer cells are constantly being released into the venous (and
lymphatic) circulation by most tumors. Larger, macroscopic
clinical palpation, assessment of mobility, and expected bio- cell aggregates may be a greater concern, however, and these
logic behavior. Some cancers deemed inoperable by imaging are may be prevented from vascular escape with early venous
in fact mobile and operable. Leading edges of some cancers are ligation.
compressed against adjacent tissue and can appear more invasive. 3. Local control of malignant cancer requires that a margin
Before declaring a mass inoperable, surgeons should always take of normal tissue be removed around the tumor. Resection
the opportunity to palpate the local tumor with the patient under of the “bad from the good” can and should be classified
heavy sedation or anesthesia before or after imaging, explore the in more detail than radical versus conservative (Table 10.1;
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history of the tumor’s growth pattern and, in many cases, obtain a also, see Fig. 10.1). Tumors with a high probability of local
tissue sample. Positive prognostic factors typically include a slow recurrence (e.g., high-grade soft tissue sarcoma, high-grade
growth rate, mobility within adjacent tissues, no previous surgery, mast cell tumors, feline injection-site sarcomas, feline mam-
discrete tumor borders, small tumor size, and a low-grade nature. mary carcinoma) should have 2 to 3 cm margins laterally
Conversely, surgery may be less effective for the same tumor type and at least one uninvolved fascial layer for deep margins.
and grade if the mass is ill defined, recurrent, or has a recent his- Tumors are not flat, and wide removal in one plane does
tory of rapid growth. not ensure complete excision. Fixation of cancer to adja-
The surgical oncologist must be able to assimilate all of the cent structures mandates removal of the adherent area en
information and make an informed decision. We must also bloc with the tumor. Invasive cancer should not be “shelled
remind ourselves and our clients that there is much we do not out” if a cure is expected. Many cancers are surrounded
know (e.g., incomplete margins do not necessarily ensure local by a pseudocapsule. This pseudocapsule is almost invari-
tumor recurrence ) and that surgical judgment regarding expected ably composed of compressed and viable tumor cells, not
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local behavior and likely resection is often qualitative and is an healthy, reactive host cells. If a malignant tumor is entered
imperfect “science.” at the time of resection or if the margins are incomplete,
The actual surgical technique will vary with the site, size, and that procedure is often no better therapeutically than a large
stage of the tumor, in addition to the skill and experience of the incisional biopsy. When possible, resection of the previous
surgeon. The same tumor type in dogs and cats may vary with scar and the entire wound bed with “new” margins (never
regard to the required surgical approach and technique and the entering the previous surgical field) is indicated, including a
prognosis. The following are some general statements that need to minimum of one tissue plane away from or deep to the mass.
be emphasized with surgical oncology. For example, invasion of cancer into the medullary cavity of
1. All incisional biopsy tracts should be excised en bloc with a bone requires subtotal or total bone resection, not curet-
the primary tumor because tumor cells are capable of growth tage. The width of surgical margins necessary for complete
within the biopsy incisions. Fine-needle aspiration (FNA) excision of a given tumor type is an ongoing debate, and our
cytology tracts are of minor, but not zero, concern, whereas current practices are based on minimal objective data. As a
punch biopsy tracts are of intermediate concern. With this in community we have answered most of the questions about
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mind, the surgeon should keep all biopsy incisions to a mini- how much tissue we can safely remove, but it will serve our
mal length and should position and orient them such that they patients well to determine how little extra tissue is neces-
can be easily removed with the definitive resection. sary to excise and consistently achieve the same success. We
2. Early vascular ligation (especially venous) should be must challenge recommendations that are reported in the
attempted to diminish release of large tumor emboli into literature if they are based solely on a surgeon’s personal
the systemic circulation. This is probably only clinically experience or opinion, in the absence of objective findings.