Basic Surgical Oncology
John D. Wooldridge, DVM, Dipl. ACVS
Neoplasia is encountered in daily veterinary practice. Advances in surgical oncology, advanced imaging techniques, chemotherapeutic options, and radiation oncology provide numerous potential treatment modalities. Surgery has a role in the management of most oncologic patients. This lecture will review the basic principles of surgical oncology, including biopsy options and techniques, staging of malignancies, perioperative considerations, principles of cancer surgery, and multimodality therapy.
Obtaining adequate tissue samples for cytologic or histologic diagnosis and grading is the first step in the management of the veterinary cancer patient. Biopsy prior to more definitive surgical excision should provide an accurate tissue diagnosis and can prevent overtreatment or the incorrect treatment. Rational decisions on the type and extent of therapy, and the likely prognosis can all be based on the biopsy results. Considerations when planning the appropriate biopsy technique include integration of the timing of the biopsy procedure into the overall diagnostic plan for the patient, the relationship of the biopsy site to subsequent surgery, proper handling of the tissue samples obtained, and providing a complete description of the clinical history, findings and suspected diagnosis to the pathologist. The biopsy site should be planned so that it can be easily excised along with the entire mass at surgery. Drains should be used sparingly, as the entire drainage tract should be considered to be contaminated with tumor cells and needs to be removed at surgery. Electrocautery distorts the cellular architecture, and should only be used for hemostasis after obtaining a diagnostic sample with a scalpel blade or biopsy punch. A tissue sample that includes the junction of normal and neoplastic tissue will provide the pathologist with the best diagnostic sample (except in bone lesions, where peripheral samples may contain periosteal reaction and yield an inaccurate diagnosis). It is important to appreciate that the depth of the sample is also important, as superficial biopsies may include ulcerative lesions and/or areas of inflammation, and may miss the deeper neoplastic tissue.
Bopsy techniques, in order of increasing invasiveness, accuracy and need for patient restraint, include fine needle aspiration, needle punch biopsy, incisional biopsy, and excisional biopsy. Fine needle aspiration is simple, fast and easy. A positive diagnosis of neoplasia can be used for therapeutic planning, but a negative aspirate or a result that does not correlate with the clinical picture necessitates repeated aspiration or use of another biopsy technique. Cutting needle or punch biopsy such as tru-cut biopsy needles for soft tissue masses, or Jamshidi needles or Michelle trephine for osseus lesions have a higher diagnostic accuracy, but greater risk of complications than fine needle aspiration. Incisional biopsy provides a larger and more representative tissue sample. Exposure of healthy tissue and neurovascular structures must be avoided, and meticulous hemostasis and wound closure must be performed. Excisional biopsy is only indicated when the treatment will not be altered by the tumor type, or when 2-3 cm surgical margins can be obtained with minimal morbidity. Unfortunately, excisional biopsy techniques are often used inappropriately.
Staging the extent of the tumor is an important therapeutic and prognostic tool, and involves examination of the local lymph nodes and determination of distant metastasis. The majority of malignancies metastasize via lymphatic or vascular routes. Methods for staging include radiography, abdominal and thoracic ultrasound, CT, MRI, nuclear scintigraphy, cytologic or histopathologic evaluation of local lymph nodes, and splenic, hepatic and bone marrow aspiration. Ventrodorsal, right and left lateral radiographic views are required for thoracic metastases checks.
Complete surgical removal of localized cancer cures more patients (human and animal) than any other form of treatment. The first surgical procedure provides the best chance for a cure, and thorough preoperative diagnosis and complete staging should be achieved whenever possible to enable the optimal surgical plan. This allows the surgeon to determine appropriate surgical margins, prepare any special instrumentation needed for resection, and minimize the sources of treatment failure. Also, knowledge and identification of paraneoplastic conditions will allow the surgeon to provide appropriate preoperative management and minimize morbidity. Potential complications must be considered; the risks of complications, and the methods of avoiding or treating complications should be assessed.
Complete patient preparation must be addressed prior to surgical intervention. The surgical site must be clipped and prepared widely to allow for changes in the surgical plan. Several methods of closure and/or reconstruction should be planned; the excision of the mass should not be unnecessarily compromised by concerns about “how to get the wound closed”. Perioperative antibiotics are indicated for most oncologic surgical procedures, and blood for transfusion should be available if needed. Palpation of the tumor should be minimized due to potential for seeding, tumor rupture, or degranulation of mast cells.
As with all surgery, the principles of “quick, clean and kind” are extremely important in veterinary oncologic surgery. In addition, the surgeon must excise all incisional biopsy and drainage tracts associated with the primary mass. The appropriate surgical margins must be determined by considering the tumor type, expected biologic behavior, anatomic location, and the barrier provided by the surrounding tissue. Tumor seeding at the surgical site must be minimized though the use of protective drapes, laparotomy sponges, glove and instrument changes prior to closure and extensive lavage; this is especially true of carcinomas of the urinary tract. Gentle tissue handling must be practiced at all times, to minimize the chances of tumor cells entering the venous or lymphatic systems during surgical manipulation, and to reduce the chances of tumor rupture. Blood vessels should be ligated as early as possible in the dissection, and always before transection. Consideration should be given to marking the deep margins of the tumor resection with radiodense materials such as staples to facilitate postoperative radiation therapy planning. An assessment of the extent of tumor excision should always be performed; the surgical cut surfaces should be inked prior to formalin fixation, and large masses may require different colors or sutures, etc., to allow the pathologist to be able to orient the sample appropriately. Finally, all resected tissue should be submitted for histopathologic analysis and margin evaluation; if it is worth cutting out, it is worth submitting.
The management of local lymph nodes is an important consideration for the oncologic surgeon, and routine staging should have indicated the presence of lymph node involvement. Lymphadenopathy of the draining lymph nodes can represent lymph node metastases (a poor prognostic sign), or hyperplasia/reactivity (which may be a beneficial host response). Lymphadenectomy is ideally performed by excision of the tumor mass, draining lymph node and all intervening lymph nodes as a single ‘unit’ (en bloc resection), although this is not often practical. In general, lymphadenectomy is NOT indicated for lymph nodes in critical areas (eg. hilar, retropharyngeal or mesenteric), where the tumor has eroded through the capsule and become adherent to surrounding structures; they should be biopsied and treated with other modalities. Prophylactic excision of normal lymph nodes is not indicated and indeed may be harmful to the patient; regional lymph nodes may initiate a desirable immune response.
When surgery alone is not curative for a particular neoplasia, treatment before or after surgery with chemotherapy, radiation therapy or immunotherapy may be indicated. While not every pet owner will be willing or able to make additional financial commitment, the surgeon must be aware of the possibility of adjunctive treatments to maximize patient care and minimize side effects. Chemotherapy is often used postoperatively, when optimal effects are directed at a reduced tumor burden. Radiation therapy is often used perioperatively, although the decision as to when to utilize radiation therapy in the treatment plan remains somewhat controversial. The use of radiation therapy is often optimized when cytoreductive surgery has reduced residual disease to a microscopic level. Postoperative radiation therapy avoids delays in surgical excision, allows accurate planning of the radiation treatment field, and avoids wound healing problems seen when operating in a previously-irradiated surgical site. In contrast, preoperative radiation may reduce the chances of viable cells being present in tumor emboli, avoids surgically-created hypoxic areas, and reduces the size of the radiation field. However, the delayed wound healing associated with surgery in a previously irradiated area means that meticulous surgical technique is required, especially with radical procedures. Consultation with a medical and/or radiation oncologist is advised as part of preoperative planning in many cases.
Mast cell tumors and vaccine-associated fibrosarcomas are two common dilemmas facing the oncologic surgeon. Strict adherence to the above principles of staging, preoperative planning, and surgery are crucial to maximize the outcome. This is especially important with tumors on the distal extremities, as excision and closure can be challenging. Mast cell tumors affecting the inguinal and perineal region are often much more aggressive clinically than those affecting other sites. Feline vaccine-associated fibrosarcomas (VAF) represent a special challenge, and adequate biopsy and staging are vital prior to surgery. Wide surgical excision (3-5 cm and 1-2 tissue planes) remains the most effective surgical approach; “shelling out” a VAF is not acceptable, and will lead to a poor result and rapid recurrence. Advanced imaging techniques such as CT and MRI often reveal a much greater tumor burden than is clinically apparent, and can help guide surgical planning. Multimodality treatment is often required to treat these types of malignancies.