Superficial Mass Resection for the General Practitioner

SUPERFICIAL MASS RESECTION FOR THE GENERAL PRACTITIONER Owen Skinner, BVSc DECVS DACVS-SA MRCVS, ACVS Fellow - Surgical Oncology

Surgical oncology is the use of surgical intervention in the diagnosis or treatment of patients with cancer. Surgical oncology is performed throughout the veterinary profession, whether in general practice or specialty centers. While most dogs (and humans) cured of cancer are treated with surgery, not all patients have disease that is treatable surgically. Furthermore, not all surgeries are equivalent. A strong understanding of cancer behavior and an understanding of cancer biology are critical to effective planning and management.

Pre-Operative Evaluation

Diagnosis - Ideally all confirmed or suspected neoplasms should be diagnosed before surgical intervention. On occasion this may not be possible, for example in the context of hemoperitoneum due to rupture of a splenic mass; however, every effort should be made to ensure that sufficient information has been gathered before committing to a management strategy. For superficial masses, fine needle aspirates and cytology will almost invariably represent the first step. If aspirates do not provide a diagnosis or if the information is insufficiently detailed (e.g. broad categories such as “sarcoma” or “malignant neoplasm”), biopsy and histopathology is indicated. Biopsies may be categorized as incision or excisional in nature. Incisional biopsies remove a piece of the mass but leave the remainder of the lesion in place. Excisional biopsies remove the gross lesion. While an excisional biopsy may seem appealing from the perspective of efficiency, if a diagnosis has not been obtained, it may not be possible to effectively plan surgical margins. This can risk undertreating due to an inadequate surgery or overtreating due to an excessively aggressive surgery or performing surgery in a patient that would not benefit from that intervention. If the clinical team is considering an excisional biopsy, all differential diagnoses should be considered. The treatment options and expected outcomes associated with those differential diagnoses should then be reviewed prior to committing to excisional biopsy. Staging – Before any major management decisions are made, a patient’s disease stage must be considered. While a patient is staged as a whole, this process can be broken into local staging, where the extent of the primary tumor is assessed, regional staging, which involves assessing draining lymph nodes for metastasis, and distant staging, where remote sites such as the lungs or liver are evaluated for evidence of cancer. Local staging may be performed via physical examination in cases with well-defined, superficial cancers. If lesions are ill-defined, deep, or fixed, cross-sectional imaging such as CT or MRI is often recommended.

The importance of regional staging depends on the behavior of the disease involved. Benign tumors or tumors that very rarely metastasize to lymph nodes, such as soft tissue sarcomas, do not typically warrant detailed regional staging. Conversely, tumors such as mast cell tumors, squamous cell carcinoma, and melanoma that metastasize commonly to lymph nodes must have regional staging to fully assess the extent of disease. Multiple options are available for regional staging, with associated pros and cons. Palpation is neither sensitive nor specific and so should not be relied on for lymph node staging. Fine needle aspirates of regional lymph nodes may be helpful but approximately a third of metastatic lymph nodes may not be identified on aspirates. In addition, patterns of lymphatic flow vary between patients and the nearest anatomic lymph node is not always the draining lymph node. Sentinel lymph node techniques may be used to try to identify the first node draining a site. A variety of sentinel techniques have been reported, including radiographic or CT lymphography, lymphoscintigraphy, and the use of dyes such as methylene blue. While promising, these techniques have yet to be fully validated in veterinary medicine. Elective lymphadenectomy may also be considered, where the regional lymph node/nodes are excised regardless of appearance based on a moderate to high risk of lymphatic spread. Ultimately, the limitations of staging the nearest anatomic lymph node(s) alone should not prevent staging if more selective techniques are not available; pretty good is rather better than nothing! Distant staging should be targeted based on the primary tumor diagnosis. Pulmonary staging with 3-view thoracic radiographs or CT is often necessary for distant staging given the high number of tumors that may develop pulmonary metastasis. This approach will not be applicable for all tumors, however. Mast cell tumors, for example, very rarely metastasize to lungs, with liver and splenic involvement most common for distant metastasis of mast cell tumors in dogs and cats.

Surgical Intent/Dose

If surgery is to be used for therapeutic purposes in dogs and cats with cancer, surgery can be considered either curativeintent or palliative. Diagnosis and staging are essential to determine an appropriate intent. Excessively aggressive surgery in a patient with advanced disease will cause undue morbidity, while assuming that only palliative options exist when disease can still be controlled can inappropriately eliminate viable treatment routes. Owner goals must be considered

when determining intent, although owners should be provided with appropriate prognostic information to ensure that these goals are realistic. The dose of surgery for tumor resection has been previously classified within the following categories: - Intracapsular resection: Dissection enters the tumor and is often likely to leave gross disease with an associated high risk of regrowth. - Marginal resection: The gross disease is excised at its margins with no or minimal normal tissue surrounding the mass. This may be sufficient for anatomically encapsulated, benign or low-grade lesions but may frequently be inadequate for aggressive masses. - Wide resection: The gross disease is excised with a barrier of normal tissue. For superficial masses, wide margins are often considered as 2-3 cm of tissue laterally and a fascial plane of dense collagenous tissue deep to the mass. - Radical resection: Resection of the entire compartment containing the mass. Surgery can also be combined with additional treatment such as radiotherapy to allow a reduced dose of surgery to provide long-term control. If the clinical team has a suspicion of needing multimodal therapy, this should be communicated to owners prior to treatment to effectively manage expectations. While revision surgery may be possible at some sites, the first surgery always represents the best chance of control; as a result, a careful diagnostic approach and thoughtful decision-making will give patients the highest likelihood of a successful outcome.

Perioperative Considerations

Contingency plans are important to allow flexibility in surgery. Anticipating potential challenges can allow preparation and prevent these challenges becoming more major issues. For example, if a superficial mass is to be resected, Plan A may be to close the site primarily. If this is not possible and the clinical team has not anticipated this challenge, options may be more limited or decisions may be made in a more stressful situation. Planning for the eventuality that primary closure may not be straightforward or feasible could allow the patient to have a wide clip and alternative management methods, such as tension-relief techniques, flaps, or second-intention healing to be considered. Tumor cells remaining at a surgery site can regrow. If margins are incomplete or if recurrence develops, the entirety of a surgical site must be revised. Keeping the surgical site as limited in size as possible within the bounds of the intended margins can limit unnecessary spread. If drains are used, they should exit close to the primary incision to avoid seeding cancer cells along the drain tract. Tumor cells can also be spread to other sites via contaminated gloves or instruments. If a tumor is diagnosed or suspected, clean gloves and instruments should be used at each surgical site to prevent spread.

Sample Handling

Almost all specimens should be submitted for histopathology following tumor resection. If it is worth removing, it is worth finding out for sure what it is. If a curative-intent resection has been attempted, cut surfaces should be marked using tissue ink, which should then be allowed to dry completely before formalin is added. Inking allows the pathologist to identify surgical margins more easily. If ink is seen to be covering cancer cells, the pathologist can be confident the resection is incomplete. Conversely, if ink is a long way from the cancer cells, that provides greater confidence that the resection is complete. Sufficient formalin must be added to allow effective tissue fixation (typically 10 times the volume of tissue). Larger specimens can benefit from incisions to allow penetration of the formalin. If the entire specimen cannot be sent out, keeping the remaining tissue in a bucket (or buckets) with formalin allows the clinical team to submit additional sections, if necessary. Framing is the context provided to a pathologist by the submitting clinical team. Framing for tumor submission should include previous diagnostic tests such as aspirate or biopsy results and clinical staging results. Describing tumor behavior, precise location, and surgical management can all provide invaluable information to a pathologist and can improve the quality of information sent back.

Postoperative Considerations

The histopathology report should be reviewed to assess whether sufficient margins were achieved to provide local control of the tumor. If margins were not sufficient, additional treatment such as revision surgery or radiotherapy may be recommended based on risk and owner goals. The type and grade of tumor should also be assessed to determine the risk of metastasis and whether additional systemic treatment such as chemotherapy would be indicated.

Final Comments

Surgery for superficial masses affords the opportunity to provide an owner with answers, control potentially lifethreatening disease, and improve or preserve quality of life. The principles used in surgical oncology are typically not complicated but being systematic and thorough can make an enormous difference in the quality of medicine provided.

MU-CVM Lectures

Aida Vientos-Plotts, DVM, DACVIM (SAIM) MU-College of Veterinary Medicine Columbia, Missouri

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