Monday, October 21, 2013

Three things I learned: surgery in small animal patients with cancer

CT is important for staging and surgical planning when removing tumours from animals. Image courtesy Dr David Simpson, Animal Referral Hospital.

Last week the AnimalReferral Hospital hosted a fantastic couple of talks for veterinarians. Medicine specialist Narelle Brown gave a comprehensive talk on hypoadrenocorticism, but today’s post will focus on the talk by Hospital Director and specialist surgeon David Simpson. He talked about surgical oncology and it’s an area of interest of mine for several reasons: a) small animal veterinarians perform a lot of oncologic surgery (the humble lumpectomy can be life-saving); b) I’ve enrolled in the Centre for Veterinary Education’s distance education program in medical oncology for 2014 as I want to try to expand my skill set for helping patients with cancer; and c) some of the oncologic surgeries undertaken by surgeons like Dr Simpson are just incredible.

The best thing about the talk was the logic and experience that Dr Simpson brought to the topic. The surgical principles are straightforward (even if the mass confronting one is not), but the way you express them can make all the difference.

Dr Simpson began the talk introducing two questions he asks in every single cancer case:
  1. What is it?
  2. Where is it?

They sound simple, but how many times do we remove a lump without the benefit of cytology or histopathology? The truth is often pathology and staging are declined by owners – which is their perogative – but in the case of malignancy it is really important.

The humble fine needle aspirate can be helpful in guiding decision making but is by no means definitive.

So what is the possible yield?

  • -      Neoplastic cells
  • -      Oil (from lipomas)
  • -      Inflammatory cells (can be associated with abscesses but also necrotic centres of tumours or mast cell tumours)
  • -      Mucus
  • -      Blood
  • -      No yield (this can happen with normal tissue but also tends to happen in the case of very fibrous tumours e.g. sarcomas, spindle cell tumours)

Dr Simpson is often requested to extend the margins of a biopsy site once histopath has returned a malignant result. He recommends making the biopsy site as small as possible and considering the ramifications for a wider resection when choosing the site. He is also very much against the use of drains in the case of narrow excisions as they increase the margins – and on a limb that can really limit options. (Of course there are some tissues where excisional biopsy of a mass is preferred: anal sacs, splenic masses, brain, thyroid and adrenal glands).

Surgical view of a massive hepatocellular carcinoma removed by Dr David Simpson. Image courtesy Dr David Simpson.

Staging helps answer “where is the mass” – and should be guided by the tumour diagnosis. For example, MCTs tend to metastasize to lymph nodes rather than the chest. Each location presents surgical challenges.

Decision making around an animal with a neoplastic mass or lump

Options
  • Do nothing
  • Palliate
  • Surgery
  • Chemotherapy
  • Radiation
  • Immunotherapy
  • Euthanasia

Factors that affect decision making
There isn’t just one way to treat a dog or cat with cancer and the truth is that many factors, physical, functional and philosophical, come into the decision making process.
  • Tumour type, stage, grade (“what is it?”)
  • Tumour location (“where is it?”)
  • The owner’s bond with the animal
  • The owner’s philosophy, biases and previous experiences with cancer in human or animal patients
  • Concurrent disease
  • Economic reality
  • Risks – morbidity and mortality associated with treatment

Dr Simpson argued that veterinarians should be clear about what they are trying to achieve with surgery and where surgery fits into the treatment plan:
  1. Diagnosis that will provide the option for more comprehensive treatment later
  2. Cure
  3. Palliative debulking (this is not ideal, wound healing may be compromised)
  4. Adjunctive to other forms of therapy.

A pulmonary adenocarcinoma removed by Dr David Simpson.
He offered several pearls of wisdom:
  • The first chance to cut is a chance to cure;
  • Avoid spreading and seedling the tumour by rough handling of tissue; avoid drains where possible; ligate the artery then the vein.
  • Try to think separately about excision and reconstruction – in major human hospitals the team that performs excision is often different to the reconstructive team. The advantage is that there is no compromise on aggressive tumour removal;
  • If it is worth removing it is worth performing histopathology [This is a mantra I personally live by…I run histopath on any lump taken off my animal because it rules out malignancy, because I know FNA isn’t perfect, and because I always learn].

Other interesting bits and bobs that I learned included that Dr Simpson now takes 2cm margins around MCTs; uses haemoclips to perform rapid splenectomise; and uses special tissue dye on large masses so when they are submitted for histopath the pathologists know the orientation of the mass. I’d never encountered the latter before and it’s a brilliant idea.

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