A Practical Guide to Veterinary Surgical Oncology:  From Pre-Op Staging to Post-Op Margins

By Dr Charles Kuntz DVM, MS, MACVSc, Diplomate ACVS, ACVS Founding Fellow of Surgical Oncology, Registered Specialist of Small Animal Surgery, Senior Staff Surgeon

When it comes to cancer surgery in pets, few things linger longer in a vet’s mind than a local tumour recurrence that could have been avoided. Incomplete surgical margins don't just compromise outcomes—they lead to repeat surgeries, emotional stress for owners, and professional frustration.

This article outlines the essential principles of surgical oncology to help ensure your first surgery is your best shot—because in cancer treatment, wide margins can mean the difference between cure and recurrence.

Cancer in dogs and cats can be overwhelming—but it isn’t always terminal. An optimistic yet realistic mindset is critical. Collaborating with pet owners to establish treatment goals, while balancing tumour biology with available therapies (surgical, medical, and radiation oncology), leads to the best outcomes.

While multimodal treatment is often required, surgery remains the cornerstone for diagnosing and definitively treating solid tumours.

• Overall health and signalment

• Concurrent diseases or conditions

Chronologic age alone is a poor predictor of surgical resilience. Physiological status matters most. Stabilising comorbidities—even if unrelated to the tumour—can significantly reduce perioperative risk.

Accurate staging is non-negotiable. It informs:

• Prognosis

• Treatment strategy

• Owner communication

Use the WHO TNM system to assess local, regional, and distant disease. A baseline diagnostic workup should include:

• Diagnostic biopsy

• 3-view thoracic radiographs 

• Fine-needle aspirates (FNA) of regional lymph nodes

Note: Palpation is not sufficient. Depending on tumour type, add abdominal ultrasound or 

CT imaging for full characterisation.

A properly planned biopsy provides critical insights into:

• Tumour type and grade

• Biological behaviour

Key biopsy principles:

• Choose tools that avoid cell damage

• Orient the incision so the tract can be excised en bloc with the tumour

• Ensure margins remain uncompromised 

Skipping biopsy planning risks misdiagnosis—and compromises definitive treatment.

Fix tissues in 10% buffered formalin (minimum 1:10 tissue-to-formalin ratio). Always provide detailed clinical history to the pathologist.

On receiving results:

• Review tumour type, grade, and margin status carefully

• Don’t hesitate to query anomalies, request re-sectioning, or seek a second opinion

Each oncology case must have a clearly defined objective - typically diagnosis, cure, or both. For localised tumours, first surgery offers the best chance of cure.

Select your approach - marginal, wide, or radical - based on:

• Tumour behaviour

• Prognosis

• Comorbidities

• Client expectations

• Adjunct therapies

Common mistake: Under-dosing. 
For malignant masses, a controlled open wound is preferable to leaving tumour cells behind.

Rule of thumb: 
Wide margins of 2–3 cm in all directions, plus fascial planes for depth, are standard for tumours prone to local recurrence.

Prepare the site with wide clipping to allow for extended margins. Address any paraneoplastic syndromes pre-op. If adjuvant therapy (e.g., radiation or reconstruction) is likely, integrate that plan early.

During surgery:

• Treat the tumour like an infectious agent—minimise manipulation

• Ligate blood vessels early

• Lavage the site thoroughly

• Use India ink to mark margins and aid histopathology orientation

Fix and label the entire excised mass with:

• Marked margins

• Accurate slicing and inking

• Clear communication with the pathologist

Pathology results guide next steps. For incomplete margins or high-grade features, consider:

• Repeat surgery

• Radiation therapy 

• Chemotherapy

Ultimately, the goal remains constant: Improve the pet’s quality of life.

Learn More: Charles' Surgical Oncology Lecture

For an in-depth discussion, access Charles’ recorded lecture on surgical oncology and wide-margin principles.: Watch the lecture  or listen to the podcast: Wide Margins Save Lives 

Need Support With a Cancer Case?

We’re here to help with any surgical or emergency oncology cases.

📧 aec.moorabbin@aecvet.com.au 
📞 03 9532 5261

DVM, MS, MACVSc, Diplomate ACVS, ACVS Founding Fellow of Surgical Oncology, Registered Specialist of Small Animal Surgery, Senior Staff Surgeon

Charles graduated from the University of Florida and did an internship at the Animal Medicine Center in New York City. He then did a residency in small animal surgery and Master’s program at Virginia Tech. Following that he did a one-year fellowship in Cardiac Surgery and Research at Auburn University and an 18 month Fellowship in Surgical Oncology at Colorado State University before he became an Assistant Professor of Orthopaedic Surgery also at Colorado State University.

Charles then started a busy referral surgical practice in Washington DC where he was also on the Board of Directors and the Program Chair for the DC Academy of Veterinary Medicine. In 2004, Charles moved to Australia and started Southpaws Specialty Surgery for Animals. He started with just one nurse and by the time he sold the practice in 2022, Southpaws was up to 170 staff over 2 hospitals. Charles set up the first radiation therapy unit for animals in Australia. He has published hundreds of articles, abstracts, book chapters and proceedings in topics related to the treatment of surgical diseases in animals. He is often invited to lecture at international conferences. Charles has 5 patents for devices used in the treatment of surgical diseases in animals.