Principles of Surgical Oncology

Elaine R. Caplan, DVM, Dipl. ACVS, ABVP
Capital Area Veterinary Specialists
Round Rock, Texas


 “Biology is King; selection of cases is Queen, and the technical details of surgical procedures are the Prince and Princesses of the realm who frequently try to overthrow the powerful forces of the King or Queen, usually to no long term avail, although with some temporary apparent victories.”

Cancer is one of the leading killers of pet animals and complete surgical resection of localized cancer cures more cancer than any other form of treatment. However, good technical skill is a small part of successful treatment of cancer. The surgeon must completely understand the anatomy, physiology, and reconstruction options for all organs. In addition, he or she must be a tumor biologist, understanding the expected biological behavior of the tumor. The surgeon must also understand the various alternative or adjuvant therapies to surgery for a particular tumor. Surgical procedures may include diagnostic, curative, palliative, or debulking. In any case, required preoperative patient planning includes diagnosis, staging, patient assessment, and treatment planning (surgery, radiation therapy, chemotherapy, etc) in order to obtain optimal results for our patients and clients.

Preoperative evaluation of the cancer patient answers the following questions:

What is it?

Where is it?

What is the status of the patient?

Tumor diagnosis is made by cytology (fine needle aspiration FNA) or histology (biopsy) of the mass. Cytology is simple and inexpensive. Round cell or descrete cell tumors can be definitively diagnosed with cytology alone. Round cell tumors include lymphoma, plasma cell tumors, histiocytoma, transmissible venereal tumor, and mast cell tumors. Discrete cell tumors include melanoma and lipomas. FNA is excellent in differentiating tumor versus nontumor (granuloma, abscess). FNA of palpable external masses is easily obtain using a 20-25 ga. needle. The needle is inserted into the mass and redirected several times by partially withdrawing and reinserting. Image guided aspirates (ultrasound, CT) of body cavity masses are also performed. Fluid aspirates can be spun to concentrate the cells (i.e. cytospin). Several unstained slides are submitted to the veterinary cytopathologist for evaluation.

Biopsy and histopathology are required for definitive tumor diagnosis and prognosis in many cases. Some owners are concerned that biopsy may cause tumor spread, however the benefits of obtaining a definitive biopsy out weigh the risks. Cell and tissue architecture is evaluated. Also malignancy can be determined by degree of tumor cell differentiation (grade) and invasion or destruction of local tissues. Grading the degree of malignancy has been found to be predictive of biological behavior. Features used to evaluate grade include:

1. degree of differentiation

2. mitotic index

3. degree of cellular or nuclear pleomorphism

4. amount of necrosis

5. invasiveness

6. stromal reaction

7. lymphoid response.

Tumor grade may correlate with survival, metastatic rate, disease free interval, or with frequency of local recurrence. Tumor grade and/or histologic features have been predictive of biologic behavior in the following tumors: mast cell tumor, lymphoma, dermal/ocular melanoma, mammary gland carcinoma, synovial cell carcoma, multilobular osteochondrosarcoma, hemangiosarcoma, transitional cell carcinoma, squamous cell carcinoma of the tongue, lung carcinoma, mandibular osteosarcoma, and soft tissue sarcoma. When reading the histopathology report, it is important to assess grade where possible or identify histological features listed above in order to determine degree of malignancy.

If the results do not fit the clinical picture, the surgeon must review the results with the pathologist and ask for a second opinion. The clinician should never hesitate to ask for a second opinion, nor should the pathologist be offended by the request. A misdiagnosis can result in unnecessary major surgery, chemotherapy, radiation therapy, or even unwarranted euthanasia.

Staging of cancer answers the question “where is it?” Staging assesses tumor size and invasiveness (T), lymph node involvement (N), and identification of distant metastasis (M). The TNM staging system is the standard adopted by the World Health Organization (WHO). Each TNM category is assigned a numerical value (1,2,3). The staging system also helps for prognosis and treatment planning. For instance, the presence of metastatic cells in the lymph node of a patient with a 3 cm³ mandibular melanoma may change the owner’s willingness to put that pet through radical surgery if the animal has a short time to live.

Local tumor (T) can be evaluated by palpation, radiographs, computed tomography (CT), ultrasound, contrast studies, or magnetic resonance imaging (MRI). Palpation of a subcutaneous mass reveals whether or not the mass is fixed to deeper tissues. Bone involvement is evaluated by radiographs or CT. The presence of bone lysis on a radiograph of a patient with acanthomatous epulis will determine the extent of mandibular resection necessary to cure that patient. In many instances, what is palpated externally is only the tip of the iceberg of how invasive the mass may be.

Lymph nodes evaluation is by palpation, FNA, or biopsy. Ultrasound, CT, or MRI can be used to identify intra-abdominal lymph nodes such as sublumbar and mesenteric. Thoracic radiographs help to evaluate sternal and tracheobronchial lymph nodes. A patient with a diagnosis of apocrine gland carcinoma (anal gland) with large sublumbar lymph nodes may require “stripping” those lymph nodes by abdominal surgery in order to get secondary hypercalcemia under control.

Metastatic disease is evaluated by physical examination, 3-view thoracic radiographs, CT, MRI, nuclear scintigraphy, abdominal ultrasound, and bone marrow aspirates. Lung is the most common site of metastasis overall. Three views should be taken since fluid gravitating to the down lung can obscure lesions due lost of contrast between fluid and soft tissue density. If an area is suspicious another set of radiographs could be taken in 3-4 weeks for comparison. CT is very useful in these situations, since there is a higher degree of sensitivity. Metastatic bone lesions (bone sarcomas, bladder/prostate/mammary carcinomas) are best evaluated by radiographs or nuclear scintigraphy (bone scan). Scintigraphy is a sensitive tool for bone metastasis and is based on associated vascular changes. Evaluating abdominal metastasis is performed by palpation, radiography, and ultrasonography. For myeloproliferative diseases (multiple myeloma, lymphoma, leukemia) and tumors that can potentially spread to the bone marrow (mast cell tumor), bone marrow aspirate and cytology are indicated.

Evaluating patient health status is important since treatment may entail general anesthesia, surgery, chemotherapy. This starts with a good physical examination, evaluating the lung sounds, heart rate and rhythm and peripheral pulse. Besides chest radiographs, echocardiogram, ECG, and blood pressure measurements may be indicated. Hemangiosarcomas may metastasize to the heart. Pheochromocytomas can cause hypertension. Laboratory data including CBC, chemistry, and urinalysis helps evaluate for issues including infection anemia,  paraneoplastic hypercalcemia or hypoglycemia, and liver/kidney function.  Coagulation is evaluated by platelet count, PT, PTT, buccal mucosal bleeding time, ACT, fibrinogen, and fibrogen degradation products. This may be required for patients with hemangiosarcoma, thyroid carcinoma, inflammatory mammary gland carcinoma, or mast cell tumor. Nutrtional status is often an issue since anorexia and cancer cachexia ar present. Often, feeding tubes are necessary.

Surgical margins are planned in advance within the normal tissue surround the tumor. The tumor must never be incised. This will result in contamination of the entire surgical site. Preoperative biopsy is essential for planning in order to know what amount of margin will assure best results. When excising a malignant tumor, 2-3 cm margins with a tissue plane deep is generally acceptable, however a feline vaccine associated sarcoma may require even wider margins. Many tumors have “tentacles” that can extend well beyond where the mass is grossly palpable. Difficult areas including the perineal region, periocular, and limbs may need preplanning for tissue reconstruction using skin flaps or grafts.

The Enneking classification of tumor resection margins describes surgical doses.


Debulking or curetting, leaves clinical disease


Within pseudocapsule or reactive zone, leaves subclinical disease (“shelled out”)


En bloc removal; margins within anatomic compartment


Entire anatomic compartment removed (amputation)


Identifying biopsy margins is accomplished when the pathologist microscopically evaluates the completeness of the resection. Margins are best identified using India ink or other commercially available dyes.  The resection closest to the tumor should be marked. The deep margins and skin margins are often inked. Black and yellow dyes stain well.

The surgeon must interpret the histopathology results critically. In human medicine, margins are considered close and probably incomplete if less than 1 cm of normal tissue is present around a malignant tumor. In veterinary medicine, if tumor cells are within 1 cm of the margin or just outside of or on the pseudocapsule, margins are called “clean, but close” or “marginal.” Immediate re-resection or adjuvant therapy (radiation or chemotherapy) may be indicated if the mass is malignant. A “clean margin” must always be interpreted with caution. The pathologist looks at representative samples. It is impossible to evaluate the entire specimen.

Advice about Curative Cancer Surgery:

1. Excise all biopsy tracts when doing definitive excision of the tumor. Keep this in mind when performing biopsies or fine needle aspirates.

2. Vascular ligation of the tumor, especially venous, should be done early in the procedure. This reduces the risk of tumor emboli release into circulation.

3. Normal tissue must be removed the tumor for good local tumor control. This is particularly important for tumors including soft tissue sarcomas, mast cell tumors, and feline vaccine associated sarcomas. 2-3 cm. margins  and a tissue plane deep is the general rule. Feline vaccine associated sarcomas have more stringent recommendations of 3-5 cm margins and 2 tissue planes deep. Structures fixed adjacent to tumors should be removed with the tumor. Malignant or biologically aggressive tumors should not be peeled out, shelled out, or curetted. The pseudocapsule surrounding the tumor contains a layer of compressed cancer cells, so normal surrounding tissue should always be removed as margins. If the tumor is entered during surgery, the entire surgical site is considered contaminated. Resection of a previous tumor scar with dirty margins involves at least 2- 3 cm margins and a tissue plane deep. The tumor bed is often marked with metal clips in case histopathology reveals dirty margins. Radiation therapy will be more efficacious knowing the extent of the wound.

4. Gentle tissue handling and copious lavage of cancer wound beds can be important to remove excess exfoliated tumor cells. Avoid entering the tumor!

5. Use separate surgical instruments for each tumor to be removed if multiple tumors are to be removed. Iatrogenic tumor spread could occur.

Lymph nodes should be removed if positive for cancer or with en bloc resection of the tumor. For example, the inguinal lymph node is often removed at mastectomy. Removal of sublumbar lymph nodes in patients with metastatic apocrine gland carcinoma generally benefit from this procedure. It may help control symptoms associated with paraneoplastic hypercalcemia.

Palliative surgery is performed to relieve pain or improve function. Improving quality of life does not always mean prolonging length the life. Splenectomy for hemangiosarcoma is a good example.

Debulking surgery is rarely indicated. The idea is to enhance the effects of other treatments such as radiation or chemotherapy. The area should be marked with metal clips for the benefit of the radiation oncologist.

Long term follow-up of a well staged, graded tumor with appropriate surgical technique and adequate tissue margins will determine success. Understanding tumor biology and using advanced imaging will help achieve maximum results.


1. Withrow SJ, MacEwan BG: Small Animal Clinical Oncology. Philapelphia, W.B. Saunders, 2001.

2. Morrison WB: Cancer in Dogs and Cats: Medical and Surgical Management. Philadelphia, Lippincott Williams and Wilkins, 1998.

3. Dernell WS: Surgical Oncology. Clinical Techniques in Small Animal Practice, 1998; 13(1).

4. Cady B: Basic principles in surgical oncology. Arch Surg 132:338-346, 1997.