It is a fact that 60% of human patients who are presently cured from cancer are cured by surgical resection alone and it is likely that the figure in veterinary patients is roughly similar. In humans there are 2 broad groups of oncologic surgeons; the generalist and the anatomic site specific. The general surgical oncologists are able to operate on most solid tumours, and have minimal experience in benign disease. Those that are anatomic site specific retain the right to treat patients with complex benign disorders related to their area of interest, i.e., orthopaedic or musculoskeletal oncologists, who will treat an array of benign bony pathologies such as bone cysts, osteomata, bone infarcts. In humans the perceived trend is towards the latter group, but generalists will likely persist given the nature and needs of health-care globally.
Veterinary surgeons are familiar with the concept of generalists and so veterinary surgeons with an interest in surgical oncology are typically involved in general oncologic surgery (benign and malignant). There is now a formally recognized surgical subspecialty (ACVS, 2011) in veterinary surgical oncology, just as there is in medical and radiation oncology.
Surgical oncology training is rooted in surgical residencies and post-residency surgical oncology fellowships but it is important to combine any training with exposure to radiation and medical oncology - major advances in these fields are dramatically changing the face of cancer treatment and the role of surgery. Cancers considered unresectable with curative intent may be brought to potentially curable surgical resection with neo-adjuvant strategies. Likewise long-term outcome for patients following local cure of a solid tumour can be significantly improved with appropriate adjuvant strategies.
Understanding the oncologic disease, rather than simply knowing how to perform a surgical procedure is vitally important to successfully manage oncology cases and advise clients. At the same time, there is a growing body of research challenging surgical dogmas about veterinary surgical oncology. An example is the rule concerning 3cm margins for mast cell tumours, that results in many patients being over-treated and large resections for low-grade masses with small tumour volumes being performed. In the future it is likely many patients will receive significantly less (but better planned) surgery than historically, with the same outcome in terms of local control.
Second to improved understanding of tumour behaviour is the role of adjuvant therapies. Whenever and wherever possible multimodality cancer therapy needs to be considered, both before, after or instead of surgery. Not only does this include medical or radiation therapies, but also immunotherapy and potentially investigational therapies, such as veterinary clinical trials.
As much information as possible should be gained on local, regional or distant spread, in particular draining lymph nodes and distant metastasis. An appreciation of tumour biology extends to a thorough understanding of biopsy techniques and principles. Creating differential lists and obtaining good imaging studies prior to biopsy will guide the surgeon on where and how to biopsy, the benefits of each biopsy type and even if biopsy is indicated. An awareness of tumour margins, compartments and likely surgical plans will also improve the quality of the biopsy, and minimise potential complications associated with it. CT and MRI are playing an increasing role in tumour staging, surgical planning, radiation planning, and outcome monitoring. It should be remembered that they can also lead to disqualification from surgery due to distribution and invasion of tumour, which may not have been apparent with radiographs and/or ultrasound.
The surgeon must have sufficient skill to succeed at surgery - typically to achieve local control of the tumour and to reduce the incidence of local recurrence to as low a level as possible. The surgeon must also ensure all of this is achieved with an acceptable quality of life. A large proportion of oncologic surgery is cutaneous and subcutaneous excisions, and familiarity, experience and confidence in reconstructive surgery is paramount. Use of random local flaps or axial pattern flaps need to follow a definitive curative-intent surgery, where there is little to no risk of residual disease. A knowledge of some of the more unusual tissue flaps is beneficial as the location and extent of wide tumour excisions can create defects in difficult locations. A good example is oro-nasal fistulae of the caudal mucoperiosteum/soft palate following maxillectomies. Reconstructive options such as bipedicle advancement flaps, temporal muscle flaps, and angularis oris APFs are all options. Cadaver work before electing to perform these flaps would be sensible.
A close working relationship between the surgeon and the pathologist is vital to provide a high quality service. If possible, spending some time (even one day) with a pathologist to observe tissue orientation, trimming, mapping, and margin evaluation is invaluable to learn how to get a greater return from your surgical specimens.
Improved surgical techniques and advances in diagnostic imaging have improved prognosis in many tumours, by reducing mortality and lowering morbidity. Notable epithelial examples include tumours of the anal sacs, liver, thyroid, urogenital system and mouth. The fate of the patient is increasingly falling back on staging and this usually impacts the decision as to whether systemic adjuvant chemotherapy is employed to prevent or delay secondary metastasis.
Research being pursued in human epithelial malignancies, especially of the breast, kidney and prostate, is the impact of finding circulating tumour cells in the peripheral blood (so-called 'blood staging'). Techniques can isolate as few as a handful of cells per 5ml of blood, and can potentially be used to stratify patients into different stages, and therefore treatments. Identifying circulating tumour cells promotes debate into their significance - Are these true metastatic deposits, or are they just cancer cells in circulation which are non-viable, with no ability to attach, invade or undergo progressive growth?
Where to Next..?
Performing bigger surgeries in the future to reduce the risk of local (or nodal) recurrence is only really justified if the current recurrence rate for a particular solid malignancy is high (> 25%). This must also be balanced against the cost, morbidity and reduced function of the larger surgery. Certainly before that is done the role of adjunctive radiation could be explored in more detail in our patients. As mentioned previously there is likely to be new research on reducing margins of normal tissue to achieve the same rate of recurrence, rather than increasing margins to lower the recurrence rate. It may be that smaller but carefully quantified margins of tumour-free tissue may be as adequate as wide excisions. In veterinary patients with short life spans, many of our patients will die from other disease before dying from recurrence or tumour-related disease and that is an important consideration in our decision making. There should not be a blind quest for clean margins in every patient. It is not the over-riding goal of surgical oncology and treatment should be tailor-made for the individual and their situation.
Other areas of expansion in surgical oncology are likely to include sentinel node studies, lymph node mapping, and non-invasive lymph node characterisation. Surgeons need to be familiar with new and emerging therapies, for example anti-angiogenic drugs, which shut off the blood supply to tumours leading to an elimination or reduction of tumour volume. Development of local therapies to reduce local recurrence (with a smaller surgery) are also likely to evolve, to include intra-arterial chemotherapy, chemo-embolisation, and isolated limb perfusion.
Radiation will evolve, for example stereotactic image-guided radiotherapy can deliver a highly conformal dose of radiation to a target, with little to no peripheral damage. Tissues which have been treated to date include brain, nose, skull, skeleton, heart-base, mediastinum, urethra, trigone and prostate. The availability of radiation will increase as will the understanding and appreciation of its roles in local cancer control.
A goal of future systemic treatment is the identification of specific groups, subsets or categories of patients/cancers that will benefit from systemic therapy, and those that will not, and refine the recommendation of universal non-specific toxic chemotherapy, i.e., strive for tailor-made adjunctive therapies. One example is appendicular osteosarcoma. Two similar patients can present with volumetrically-equivalent distal radial osteosarcoma; bone scans and thoracic radiographs can be unremarkable at time of amputation. Both could receive conventional chemotherapy and one suffer lung metastases at 150 days and the other be tumour free at 600 days. Arguably the first patient could be spared the time, expense, and toxicity of chemotherapy for a comparatively small increase in survival over amputation alone.