Therapeutic Modalities: Surgery
Generally, if a primary tumor can be completely excised “en bloc” with acceptable morbidity, surgery is the best treatment. The first attempt at surgical excision always offers the best opportunity to completely remove the tumor. For this reason, appropriately assessing the patient before surgical excision of a mass is indicated (see Tumor Diagnostics and Staging).
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Locally recurrent tumors are often more difficult to remove than the initial tumor because more extensive involvement of normal tissues in the region occurs and normal tissue planes are distorted by scar tissue.
An en bloc excision is derived from French, meaning “as a whole.” In surgical oncology it refers to the removal of a margin of healthy tissue (e.g., normal skin, muscle) around the tumor in one piece, having never cut into the tumor itself.
For tumors that are large, fixed, or located adjacent to critical normal structures, preoperative CT or MRI may be helpful in planning the surgical excision.
The usual objective of surgery is to obtain wide surgical margins in all directions surrounding the tumor; that is, to remove the tumor with a grossly visible intact cuff of surrounding normal tissue. The necessary margin often depends on the tumor type and, in some cases, the tumor grade, as well as the type of tissues that are adjacent to the tumor. For example, fascial planes generally provide a good physical barrier to tumor growth, so excision of an intact fascial plane below a tumor is an excellent way to optimize the chance of a complete excision. Subcutaneous fat is poorly resistant to tumor growth and should always be aggressively excised with the tumormass.
A marginal excision refers to ‘‘shelling out’’ a tumor or excising it just outside its pseudocapsule. Because the pseudocapsule often consists of compressed cancer cells, marginal excisions risk leaving microscopic quantities of tumor cells in the patient and are associated with higher rates of local recurrence than wide excisions. As a rule, marginal excisions should be avoided when possible unless postoperative RT is planned, or if the client’s only goal is temporary palliative care for a local tumor causing concerning symptoms, with no foreseeable plans of pursuing additional definitive therapies.
Although most general surgery principles apply to oncologic surgery, a few additional practices to implement in cancer surgeries are listed in Table 5.7.
All excised tumors should be submitted for histopathologic examination and margin analysis. Because pathology laboratories typically prepare representative samples from a given specimen, a report of complete margins does not necessarily guarantee that an excision was complete. A report of incomplete margins means the resection was histologically incomplete in at least one location. Although overall recurrence rates are consistently greater for tumors with incomplete margins than for tumors with complete margins, clients should be aware that tumors with complete margins can recur locally and, conversely, many tumors with incomplete margins do not recur. Following a report of incomplete margins, options include close monitoring (if an appropriate re-excision will be feasible should local recurrence develop), immediate wide excision of the surgical scar, or postoperative RT.
TABLE 5.7 Special Considerations in Oncologic Surgery
Principles of Oncologic Surgery |
Rationale |
Examples |
|---|---|---|
Complete tumor excision with adequate margins when possible |
Adequate excision decreases the risk of tumor recurrence. |
Adequate margins vary by tumor type; examples include:
|
Ink specimen margins |
Allows pathologists to distinguish actual margins from margins introduced during tissue processing. Also allows identification of which margins were closest, narrow, or incomplete. |
Identify deep margin, lateral margins, proximal/distal, cranial/caudal, and dorsal/ventral as appropriate to the site. |
Add markers/ hemoclips around the surgical field |
If postoperative imaging and radiation are pursued, such markers can aid in defining the target and act as fiducial markers for treatment setup. |
Mark the circumference and deep margins of the surgical field. |
Assess lymph nodes |
Lymph node biopsy or excision is frequently a helpful and prognostic staging test that can be performed at the time of surgery. |
Examples include:
|
Minimize tumor seeding and contaminating other tissues |
Tumor cells are easily seeded on instrument tracks and throughout the surgical site during mass removal. Seeding can result in regional recurrence. |
|
Reconstruction and function preservation |
Reconstruction should preserve function and minimize tension to the greatest extent possible. It should consider the impact of reconstruction on additional therapy (i.e., second surgery or radiation therapy). |
In general, orient incisions along naturally existing tension lines, dependent on location. For example, orient incisions on the limb from proximal to distal rather than circumferentially. |
The 2026 AAHA Oncology Guidelines for Dogs and Cats are generously supported by CareCredit, Hill’s Pet Nutrition, Merck Animal Health, and Zoetis.
