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
228
