Veterinary Surgical Oncology. Группа авторов

1 Principles of Surgical Oncology

       William T.N. Culp and Nicole Ehrhart

      Cancer treatment is a rapidly changing and evolving area involving multiple diagnostic and therapeutic modalities to achieve the most optimal outcome. Surgical intervention remains a pivotal aspect of the treatment of cancer. Surgery cures more solid cancers than any other single modality. Nonetheless, the optimal treatment pathway for any given animal patient with cancer most often involves several adjuvant treatment modalities. Adjuvant treatments significantly affect the success of surgery, and likewise, surgery affects the outcome of adjuvant treatments. It is widely recognized in human cancer centers that patient outcome is greatly improved when surgery is performed by a surgeon with specialized training in oncologic procedures. Surgeons trained in these programs have expertise in the selection of surgical treatment options in combination with other forms of cancer treatment, as well as knowledge of the benefits and risks associated with a multidisciplinary approach beyond what can be mastered within a three‐year surgery residency training program. This level of expertise requires an understanding of the fundamental biology of cancer, clinical pharmacology, tumor immunology, and endocrinology, as well as a thorough understanding of potential complications of multimodality therapy. Veterinary training programs in surgical oncology have been in existence for almost 20 years. With the development of novel treatments, the role of the surgical oncologist is constantly evolving and changing (O’Reilly et al. 1997; Drixler et al. 2000).

      Therapeutic goals (e.g. curative‐intent, cytoreduction, or palliation) for each case should be established with owners before surgery is initiated. The efficacy of surgical therapy in any patient with cancer is heavily dependent upon the surgeon’s global understanding of the patient’s general health status, lifestyle and activity level, type and stage of cancer, adjuvant therapies available, alternatives to surgery, and expected prognosis. To maximize effectiveness, the optimal treatment pathway for each case should be strategically assessed prior to initiating treatment. This planning should always include a frank and thorough discussion with the owner regarding preoperative diagnostic tests, stage of cancer, palliative options, surgical options, adjuvant treatments likely to be needed, costs, postoperative care and expected function, cosmesis, and prognosis including risks of complications. The goal of this discussion is to provide the owner with enough information to help them make an informed choice regarding the best treatment pathway for their companion. Highly individualized initial planning will allow for the best overall outcome for each patient.

Preoperative Considerations

      Signalment

      The patient’s age, gender, breed, and weight are important factors in the determination of appropriate recommendations. Advanced age is not necessarily a negative prognostic factor. Comorbidities common to geriatric veterinary patients such as renal insufficiency, hepatic disease, or osteoarthritis may limit or change specific treatment recommendations; however, the age of the patient alone should not.

      Certain neoplastic diseases are common in a particular gender or breed. The surgical oncologist should always bear in mind the role that gender and breed play in the diagnosis of neoplasia. As an example, the differential list for a flat‐coated retriever with a femoral bony lesion noted on radiographs that has been referred for a suspected diagnosis of osteosarcoma should be expanded to include histiocytic sarcoma; other diagnostics such as an abdominal ultrasound would be recommended to look for other foci of histiocytic disease.

Other portions of the signalment are also important to note, including the patient’s weight and body condition. Patients that are morbidly obese or those in poor body condition may not be able to function effectively or may be more severely debilitated by a major surgery. For example, a patient with cancer cachexia can have such profound alterations of their carbohydrate, protein, and fat metabolism that recovery may be compromised (Ogilvie 1998).

      Staging/Concomitant Disease

      Staging diagnostics such as a complete blood count, chemistry profile, urinalysis, thoracic radiographs and abdominal ultrasound, and/or thoracic and abdominal computed tomography (CT) are essential components for the preoperative assessment of veterinary oncologic patients. While there is debate about the timing of some of these diagnostics (i.e. before or after biopsy), for many patients, thorough preoperative staging diagnostics can unmask an underlying condition that may alter the plan or better assist the surgeon in providing a more accurate prognosis. Alternative surgical dose may also be recommended based on the results of staging.

      Neoadjuvant Therapy

      The surgical oncologist is often presented with extremely large tumors or tumors located in difficult anatomic locations. It is important to consider neoadjuvant treatments, if available and warranted, such as chemotherapy and radiotherapy before proceeding with surgery. In some cases, these treatments may decrease the overall surgical dose needed to achieve local control. Most commonly, recommendations about chemotherapy and/or radiation therapy are made after the grade of the tumor and the surgical margins have been determined. In tumors that are suspected to be sensitive to chemotherapy based on published literature or previous experience, a postoperative protocol can be discussed prior to surgery.

      Neoadjuvant chemotherapy is rarely pursued in veterinary medicine. However, for certain tumor types, this may prove to be a beneficial adjunct to surgery. In human cases of osteosarcoma, neoadjuvant chemotherapy is commonly used prior to surgery and local tumor response (as measured by percent tumor necrosis) has been shown to be associated with increased survival. A veterinary study showed that neoadjuvant chemotherapy with prednisone administered to a group of dogs with intermediate‐grade mast cell tumors resulted in tumor size reduction; surgical excision of very large mast cell tumors or tumors that were in an anatomic site that precluded wide (3 cm lateral and one facial plane deep) excision was more successful (Stanclift and Gilson 2008). Microscopically complete margins were achieved in many of the pretreated cases. These patients would not likely have had complete surgical margins otherwise (Stanclift and Gilson 2008). Long‐term follow‐up was not the focus of this study, however, and controversy exists as to the risk of local recurrence in patients where neoadjuvant chemotherapy is used to shrink gross tumor volume with a view to allow a less aggressive surgical margin. Further study is needed to assess the benefit of neoadjuvant chemotherapy in veterinary cancer patients.

      Neoadjuvant radiation therapy has also been advocated as a method of treating neoplastic disease to reduce the need for radical surgery (McEntee 2006). Advantages to neoadjuvant radiation therapy include a smaller radiation field, intact tissue planes, better tissue oxygenation, and a reduction in the number of viable neoplastic cells that