Chapter 32: Surgical Oncology Principles

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Surgical Oncology Principles

Animals with cancer often have advanced (locally invasive or metastatic) disease. Veterinarians consulting with owners must have a strong knowledge base regarding the behavior of the tumors that commonly occur in dogs and cats. Insufficient knowledge may preclude the appropriate diagnostic testing and procedures commonly performed by oncology specialists. Many tumors demand an aggressive surgical approach that requires an experienced operator. In these cases, referral to a specialist should be considered because the best chance to remove a tumor is the first attempt. In addition to knowing when tumor resection is possible, clinicians must realize when the extent of disease has become too advanced to recommend surgical treatment. Veterinarians always must be mindful of the impact of any intervention on the quality of their patients’ lives. Convincing owners of the importance of quality of life can be a difficult task when owners struggle to accept the limitations of the therapies currently available.

Tumor Excision

One fundamental of oncologic surgery is an understanding of the classification scheme that describes different types of tumor excision. This nomenclature, published by Enneking (1983), is an important means of communication between oncologists. It also helps the surgical oncologist categorize levels of tumor excision and have a clear goal for the amount of tissue that must be excised in the context of the overall treatment plan (e.g., when the combination of surgery and radiation therapy [RT] is being considered).


A wide excision is removal of the mass, pseudocapsule, reactive zone, and an additional margin of normal tissue (e.g., 2 to 3 cm) or an anatomic mesodermal barrier to tumor cell migration such as fascia, cartilage, or bone. Because the entire tissue compartment (e.g., entire bone or muscle belly) is not removed, it is possible that “skip” metastases (satellite tumor colonies nearby but separate from the primary mass) could be left behind. Through the years, the 3-cm margin rule plus a deep fascial plane has been accepted by most surgeons for tumors such as mast cell tumors (MCTs) and STSs. More recently researchers suggested that 2-cm margins may be satisfactory for grade I and II MCTs (Simpson et al, 2004) and that the grade of a given STS may be important to determine margin width. For example, low-grade STSs may require smaller margins, whereas other tumors such as vaccine-associated sarcomas call for maximal margin width (e.g., 5-cm skin margins and two layers of fascia) because of the tumor extension along fascial planes.

Understanding Tumor Biology

All tumors are not created equal, and even within the benign and malignant categories tumor behavior varies. The surgeon must be familiar with the biologic behavior of the individual tumor types because tumor identity affects many aspects of case management. In general, carcinomas metastasize via the lymphatic system, and sarcomas via the hematogenous route. However, the two vascular systems are connected by lymphovenous communications, and there are exceptions to these patterns. A strong knowledge base enables the surgeon to perform thorough physical examinations and educate the client about tumor behavior (e.g., degree of local invasion, patterns of metastasis), important staging tests, the type of resection required for cure, and long-term prognosis. Perhaps the best example of the importance of understanding tumor behavior is illustrated by the behavior of appendicular osteosarcoma. In these cases the client must understand that, despite “clean” chest radiographs, dormant micrometastasis in the lungs likely is present and that the possibility of cure is extremely low. Understanding tumor behavior helps guide these preoperative staging evaluations.

Client Communication

The surgeon must develop a good relationship with the client and communicate effectively. Owners of pets with cancer often are anxious and overwhelmed about the condition of their pets, which makes effective communication challenging. Given the aggressive nature of some surgical resections (e.g., nasal planum resection), surgeons should prepare clients for the expected postoperative appearance of their pets. To do this, clinicians can create an image library depicting immediate postoperative and follow-up appearance from other cases. Clients must have a good understanding about the patterns of the disease, the likelihood of local recurrence, and the overall prognosis.

Almost as important as knowing when to recommend surgery is knowing when the disease state is too advanced to warrant surgery or will cause the patient to have a poor quality of life because of the extent of the resection. For example, resection of a large thyroid carcinoma that is fixed and invading underlying tissues likely would be incomplete and associated with significant hemorrhage and high morbidity. Furthermore, this surgery likely would not be curative because of local tumor thrombi and/or metastatic disease. The value of this determination cannot be overemphasized, and the ability to communicate this effectively to clients is crucial. Reactions from clients vary greatly regarding their view of acceptable surgical procedures. Some clients may be comfortable with radical laryngectomy and a permanent tracheostomy for a laryngeal neoplasm; others will not consider limb amputation because they cannot bear the thought of seeing their pet with such an altered appearance. Clients who initially are reluctant to have a certain procedure performed often change their minds once they have had a chance to reconsider the information or speak with another client whose pet was treated similarly. However, the surgeon must not impose a decision on clients who are undecided about surgery and make sure the client is comfortable with the plan. Many veterinary cancer centers use mental health professionals to assist with the surgeon-client communication and provide support to clients during the decision-making and/or treatment process.

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Jul 18, 2016 | Posted by in PHARMACOLOGY, TOXICOLOGY & THERAPEUTICS | Comments Off on Chapter 32: Surgical Oncology Principles
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