Principles of Surgical Oncology in Dogs and Cats
World Small Animal Veterinary Association World Congress Proceedings, 2009
Felipe Wouk, DVM, MSc, DrSci
Full Professor of Surgery of the Department of Veterinary Medicine, Federal University of Paraná, Brazil

Oncology is a science which investigates the pathological phenomenon of uncontrolled cell proliferation in all its multifactorial aspects.

Surgical oncology, as its name suggests, is the specific application of surgical principles to the oncologic setting. These principles have been derived by adapting standard surgical approaches to the unique situations that arise when treating cancer patients.

Cancer is one of the most common causes for mortality of small animal companion animals. The role of the surgeon is important in the treatment of cancer because it often provides an immediate cure. Cure is defined in terms of the tumor-free interval the specific cancer associated with a negligible chance of recurrence. Disease-Free Interval of three years or more after treatment of most solid cancers in small animals are associated with so few clinical recurrences that is safe to assume the patient will never be bothered by that tumor again.

Surgery can be the sole source of treatment or can be combined as part of a multidisciplinary protocol including chemo, immuno, and radiation therapy. Surgery can be used to obtain a diagnosis, a complete cure of the disease, to stage the tumour, for palliation, and for debulking (cytoreduction) in combination with another treatment modality.

Diagnosis of the type of tumour can be obtained by fine needle aspiration and cytological examination. However, histological evaluation of a biopsy specimen allows a more definitive diagnosis. A biopsy specimen can be obtained using a needle or skin punch biopsy instrument or an incisional and excisional, surgical biopsy technique, biopsy techniques under endoscopic, laparoscopic, and diagnostic imaging.

General rules for biopsy:

1.  The tissue removed should be representative of the whole lesion.

2.  Avoid zones of hemorrhage, necrosis, and obvious infection.

3.  Avoid crushing and charring of removed tissues.

4.  Include healthy marginal tissue: lesions of skin and mucosal surfaces.

5.  Avoid massaging cancer cells into the circulation.

6.  Avoid direct implantation of released malignant cells into adjacent healthy tissue.

7.  Avoid repeated biopsies of the same lesion.

Fine Needle Aspiration Biopsy (FNAB)

FNAB is best performed using a 22 G. needle and a 10 ml syringe. Tumour cells are aspirated by applying suction and gentle manipulation of the needle in the tumour tissue. Cytology allows a quick diagnosis of exfoliative tumours. Mesenchymal tumours may be hard to diagnose using this technique.

Core Needle Biopsy

A core needle obtains a cylinder of tumour tissue. The needle is inserted into the tumour after the animal has been sedated. The stilet of the needle is pushed into the tumour and a core of tumour is trapped in the recess of the needle after the outer cutting layer of the needle is advanced over the stilet. The needle is then withdrawn from the tissue. Histological examination of the biopsy specimen will allow diagnosis in most tumours. Tough connective tissue tumours and blood-filled tumours may pose a problem.

Incisional and Excisional Biopsy Techniques

Larger amounts of tissue can be obtained by incisional and excisional biopsy techniques. These techniques will allow better evaluation of tumour characteristics, including margins, but require general anesthesia. Excisional biopsies are performed in areas where the tumour can be easily removed using adequate margins or in case of benign lesions. Incisional biopsy techniques are best used for large tumours, or for tumours located in places where wide excision is not possible. The location of the biopsy incision is of extreme importance, because it needs to be excised during later surgical procedures.

The usual indication for biopsy of the lymph node is to establish the diagnosis of lymphoma or metastatic carcinoma. Each situation should be approached in a different manner.

The goal of biopsy in the patient with an abnormal lymph node and suspected lymphoma is to make the general diagnosis and to establish the lymphoma type. Consequently, the initial diagnosis of lymphoma should be made on a completely excised node that has been minimally manipulated to ensure that there is little crush damage. When primary lymphoma is suspected, the use of needle aspiration does not consistently allow for the complete analyses described above and can lead to incomplete or inaccurate diagnosis and treatment delays.

The diagnosis of metastatic carcinoma often requires less tissue than is needed for lymphoma. Fine-needle aspiration (FNA), core biopsy, or subtotal removal of a single node will be adequate in this situation. For metastatic disease, the surgeon will use a combination of factors, such as location of the node, physical examination, and symptoms, to predict the site of primary disease. When this information is communicated to the pathologist, the pathologic evaluation can be focused on the most likely sites so as to obtain the highest diagnostic yield. The use of immunocytochemical analyses can be successful in defining the primary site, even on small amounts of tissue.

For soft-tissue or bony masses of the trunk or extremities, the biopsy technique should be selected on the basis of the planned subsequent tumor resection. The incision should be made along anatomic lines in the trunk or along the long axis of the extremity. When a sarcoma is suspected, FNA can establish the diagnosis of malignancy, but a core biopsy will likely be required to determine the histological type and plan neoadjuvant therapy.

The surgical planning for the operative procedure should be made carefully. The best, and often the only, opportunity for cure is at the time of the first surgery. Enucleation or incomplete excision of tumor masses is never indicated as a therapeutic measure.

There are major determinants of operative risks: General health status, severity of underlying illness, degree to which surgery disrupts normal physiologic functions, technical complexity of the procedure (related to incidence of complications), types of anesthesia required, and experience of the personnel.

Preoperative preparation of the patient should consider that tumor acts as a nitrogen trap because of its rapid growth as the metabolic expense of the rest of the body. It is important to evaluate serum albumin and if necessary give IV hyperalimentation. Particularly in gastrointestinal cancers due to bleeding anemia is often present and as necessary measure blood volume and replace blood or red cells deficit. In the elderly patient associated cardiovascular and pulmonary disease may be present, which should be treated preoperatively guided by thoracic radiographs, ECG, BUN, and electrolytes if vomiting is present. Rule out obvious possible sites of metastases such as liver, lung and bones where indicated by checking skeletal and thoracic radiographs, abdominal US and liver chemistries.

The extent of surgery depends on the type and stage of the tumour. A pre-resection biopsy is often necessary to anticipate sufficient margins of resection and behavior of the primary tumour. Staging the tumour will prevent treatment failures caused by early metastasis and will help in deciding the type of resection and use of adjuvant treatment modalities. For some tumour types, histological grading may be valuable to anticipate the prognosis after surgery. Diagnosis of intercurrent diseases often will alter surgical treatment options and should be evaluated beforehand to assess the risk versus benefit of surgical intervention. The surgical field should be prepared carefully to allow changes in the extent of resection based on new information obtained during the operation. The risk of microfocal, regional or distant dissemination generally increases with the advancing clinical and pathological stage of disease. Later the disseminated phase is reached, better the diagnosis. This concept indicates the need to attack a cancer during its local and regional phases providing "wide local excision" with resection of the primary lymphatic drainage

Surgical Technique

Oncologic surgery often combines many surgical specialties. Knowledge of general, orthopedic, reconstructive, and oncologic surgical techniques will need to be combined with a solid anatomical knowledge base to prevent unpleasant and unnecessary surprises. Dissection of tumours should be clean and exposure of the tumour should be prevented. Tumour cell contamination (seeding) is minimized by avoiding tumour incision, shielding normal tissue by protective covering, and using proper electrosurgical techniques. In case of contamination, contaminated sites should be resected (where possible), the wound should be lavaged, and contaminated gloves, drapes and instruments replaced. Adjunctive therapy often is indicated in these cases. Tissue handling should be according to Halstead's principles and the tumour itself should be handled as little as possible. Neovascularization is often prominent and should be dealt with properly by electrocoagulation or suture ligation. Tissues macroscopically invaded by the primary tumour should be excised 'en bloc'.

Surgery for Cure

Resection for cure must be aggressive and at an early stage of disease. The most important theme for oncologic surgical management is that the first time has the best chance of curing the patient. Margins should not be compromised because it is better to leave a wound open to heal by second intention than to leave tumour cells behind. Recurrent tumours are always more difficult to treat than the primary ones. Familiarity with tissue grafts, skin flaps and other reconstructive techniques will allow wider resections, minimize patient morbidity (and in the end patient mortality) and decrease the temptation to compromise the resection, and thus recurrence.

Surgery for Palliation

The goal of palliative surgery is to improve the quality of the patient's life, without the guarantee that it will increase the survival time. This type of surgery demands a very careful consideration of the risk versus benefits but will be beneficial for certain patients (e.g., amputation of an extremities face a metastatic osteosarcoma).

Surgery for Cytoreduction

Incomplete removal of the tumour is only beneficial in cases in which total resection is not possible, in which adjunctive therapy may benefit from the procedure, and in cases of severe morbidity caused by the primary tumour. Cytoreduction is, however, rarely indicated and should be avoided.

Surgical Margins

Surgical margins are dictated by the tumour type and grade, and the anatomical location of the tumour. The most rational approach is to think of biologic rather than geometric margins and to combine this information with the expected growth behavior of the given tumour type. Tumours with high probability of local recurrence (e.g., mast cell tumours, feline mammary tumours) should have 2 to 3 cm margins removed three-dimensionally. Collagen/matrix-rich and poorly vascularized tissues are least vulnerable to tumour invasion and may be used for margin determination. All previously performed biopsy tracts should be removed in continuity with the primary tumour to prevent tumour seeding. With a proper resection the tumour is never visualized.

Postoperative Care

Supportive care is provided as necessary for vital organ function, nutritional support, and wound healing. Appropriate pain management is essential and often neglected. Resected tumour specimens should be sent for histological examination to evaluate tumour type, grade, and surgical margins. Questionable results are discussed with the pathologist. Long-term monitoring includes regular examinations to facilitate early detection of tumor recurrence. Follow up do includes rehabilitation by different physiotherapy techniques.


In veterinary medicine 80% of the cases of companion animal cancers are treated by surgery and surgery is employed in 100% of diagnostic and statement situations. Correct and aggressive surgical resection after a solid diagnosis in an early stage of the disease will be associated with the best results.


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2.  Dernell W. Surgical oncology. Clinical Techniques in Small Animal Practice. Vol. 13, n1, p.1-76, 1998.

3.  Hawkins EC, Morrison WB, Denicola DB. Cytology analysis of bronchoalveolar lavage from 47 dogs with multicentric malignant lymphoma. Journal of the American Veterinary Medical Association. Vol. 203, p. 1418, 1993.


Speaker Information
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Felipe Wouk, DVM, MSc, Dr.Sci
Department of Veterinary Medicine
Federal University of Paraná

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