Introduction
Surgery continues to be the most effective option for the management of cancer, with clinical cures more commonly achieved by surgical removal of localised disease than with any other treatment modality. However, success can often be dictated by the extent of the surgery performed. One of the golden tenets of oncologic surgery is: “the first time to cut, is the best time to cure.” Subsequent surgeries following an incomplete resection are more likely to be associated with tumour recurrence, or may require the patient to undergo a much more extensive surgical procedure than would have otherwise been required.
Before the first incision is made, the surgeon must consider the ‘dose’ of surgical intervention required i.e. how much tissue needs to be removed along with the visible mass? Only by knowing the tissue diagnosis and biological behaviour of the cancer can this decision be reliably determined. In almost all instances, a cancer surgeon will try to operate with intent of achieving successful elimination of the tumour.
Pre-operative assessment
Before undergoing surgery, the cancer patient should undergo a complete physical examination to detect concurrent disease. Some tumours cause specific clinical disease (paraneoplastic disease) that may complicate the management of the case.
If the cancer is considered malignant, accurate staging of the tumour is essential to provide accurate prognostication. This requires examination of local and regional lymph nodes (N), and determination of distant metastases (M) by a combination of imaging modalities.
Surgical treatment of cancer
Surgical management of cancer can be divided into the following categories:
- Curative-intent
- Cytoreductive
- Palliative
- Prophylactic
Curative-intent surgery
In most instances where a tumour is localised, surgery will be performed with curative intent. This doesn’t mean that a cure is certain. Curative-intent surgery defines a strategy where the surgery is carefully planned to ensure that all of the tumour is removed together with an adequate buffer of normal tissue to help prevent recurrence. The amount of normal tissue that needs to be removed about an individual tumour is not well-defined, but guidelines do exist. These can be broadly categorised as follows:
Local excision
With local excision, the surgical dissection plane is directly onto the tumour capsule and the mass is ‘shelled-out’ from the surrounding tissue. Local excision of a tumour is the least invasive, and therefore, often the easiest surgical option. However, it is likely microscopic disease will remain within the tumour bed, so local excision is usually limited to benign tumours with negligible risk of recurrence. It is contraindicated for all malignant and invasive benign tumours.
Tumours amenable to local excision include lipoma, histiocytoma, and most adenomas
Wide, local excision
For benign tumours that do not have a distinct capsule, excision of the tumour together with a margin of normal tissue is indicated. The amount of the normal tissue that must be included in the resection is dictated by the histological diagnosis of the tumour, its’ histological grade and anticipated local invasiveness. A margin of 2 cm is often quoted, but with higher grade malignancies, a much wider margin may be required to ensure all microscopic disease is removed.
All resected tissue is submitted to a pathologist to allow a histological diagnosis on the tumour to be obtained, but also for the tissue margins to be examined specifically to ensure complete resection has occurred.
Compartmental resection
Successful treatment of some tumours requires complete removal of all apparently normal tissue, including blood vessels, nerves etc contained within an anatomical compartment about all three dimensions of the tumour. Careful pre-operative planning is required to ensure the resection can proceed without compromise to essential organs, and that successful closure or reconstruction of the resulting deficit can be achieved.
Cytoreductive surgery (Debulking)
Sometimes, surgical resection alone is unable to achieve complete removal of the tumour burden. This may be because either the tumour location precludes extensive, compartmental resection without compromising normal, essential organs, or the biological behaviour of the tumour is aggressive with extensive local invasion and/or distant metastasis. In these cases, optimal cancer therapy is obtained with surgery in combination with radiotherapy, and/or chemotherapy. By combining these treatment modalities, superior cancer control can be obtained whilst avoiding disfiguring or debilitating surgery. However, consideration of their use should be made either pre-operatively or in the immediate post-operative period (e.g. if histology has reported an incomplete resection). Maintaining a ‘wait-and-see’ approach allows microscopic disease to develop into macroscopic disease, and the window of opportunity has been lost.
Palliative surgery
Some cancers carry a hopeless prognosis, usually because of a tendency to metastasise early in their clinical course. In these cases, aggressive ‘curative-intent’ management of the primary lesion is pointless, as the animal will ultimately die from diffuse neoplasia. However, palliative removal of the tumour burden may restore or maintain a quality of life acceptable to the owner until euthanasia becomes inevitable. This interval may also provide the owner with an opportunity to come-to-terms with the prognosis and thus facilitates the grieving process.
Examples of palliative surgery include amputation of a primary bone tumour which is causing pain or lameness; removal of a large, ulcerated mammary carcinoma causing systemic illness; hemi-mandibulectomy for aggressive oral neoplasias; splenectomy for a haemorrhaging haemangiosarcoma; partial pancreatectomy for insulinoma.
Prophylactic surgery
Some common cancers in dogs and cats can be prevented. An example of a prophylactic oncologic procedure is ovariohysterectomy of the bitch to prevent the development of mammary tumours. Other examples of prophylactic surgery include castration to prevent perianal adenoma and testicular cancer (especially if monorchid); removal of colonic polyps.
Conclusion
Surgery remains the most powerful weapon in the battle against cancer. Used appropriately, surgery can achieve clinical cures of seemingly large and aggressive lesions. However, if used inappropriately, surgery can complicate the management of smaller and seemingly less aggressive lesions, making clinical cure impossible. The first and best chance to cure cancer is at the initial surgery. It is important to make sure this chance is used wisely.