INTRODUCTION

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, is noncarcinogenic, less immunosuppressive than other cancer treatments, and is generally more effective than chemotherapy and radiation for treatment of certain large, localized tumours. However, if applied in an incorrect manner, surgery can do more harm than good and in performing this type of surgery the surgeon must adhere to correct (oncologic) surgical techniques and must have an adequate knowledge of the tumour type and biologic behaviour.

Goals of surgery

The goals of surgery may vary and it is important to establish these goals before initiating any therapy. Also, the goals of the surgeon may differ from those of the owner and owner's expectations should be established beforehand. 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

Diagnosis of the type of tumour can be obtained by fine needle aspiration and cytological examination. However, histologic 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 may further enhance the final outcome.

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. After this, the suction is released, the needle withdrawn from the tissue and the contents of needle and hub are squirted on a slide and submitted for cytologic examination. Cytology allows a quick diagnosis of exfoliative tumours. Mesenchymal tumours may be hard to diagnose using this technique.

Tru-cut needle biopsy

A Tru-cut 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. Histologic 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 anaesthesia. 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.

Surgical planning

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 behaviour 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, histologic 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.

Surgical technique

Oncologic surgery often combines many surgical specialties. Knowledge of general, orthopaedic, 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. Neovascularisation 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., splenectomy for an acutely bleeding hemangiosarcoma of the spleen).

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 behaviour 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 vascularised 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 histologic 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 tumour recurrence.

CONCLUSION

Surgical therapy of companion animal cancer is an important treatment modality. Correct and aggressive surgical resection after a solid diagnosis in an early stage of the disease will be associated with the best results.

References

1.  Biopsy techniques for use in small animal oncology. J Am Anim Hosp Assoc 1981;17:889-902.

2.  Surgical Oncology. In: Withrow SJ, MacEwen EG (eds). Small Animal Clinical Oncology, 2nd ed. WB Saunders Company, Philadelphia 1996:58-63.

3.  Surgical Oncology. Vet Clin North Am Small Anim Pract 1995;25:1