Surgical Margins

Classical margin evaluation with a metric radial margin and a fascial plane deep to the tumor must be adjusted in the assessment of margins for solid carcinomas such as thyroid carcinoma, anal sac adenocarcinoma and thymic carcinoma. If these tumors are marked with tissue ink and submitted for histopathology, it is possible that a pathologist may report a metric margin and that this margin, if 0-2mm, may be interpreted as a dirty margin. More work in the reporting of the margins of these tissues is required, with very little information available in the veterinary literature. In human evaluation of thyroid carcinoma, the focus is on whether or not there is extracapsular extension of the tumor. This is a more appropriate way to evaluate the completeness of excision in solid carcinomas. For any of the solid carcinomas listed above, an en bloc excision with 3cm margins and/or a true fascial plane surrounding the tumor is not feasible. However, without extracapsular extension, the rate of recurrence in these tumor types is low, with failure more commonly due to metastatic disease.

Another question that arises in the surgical planning for complete margins of excision is whether or not neoadjuvant therapy is worthwhile pursuing prior to excision. The most common tumor type in veterinary medicine where neoadjuvant therapy has been attempted for local downstaging is mast cell tumors. The use of neoadjuvant therapies remains somewhat controversial and the use of preoperative therapies may depend to some extent on the goals of surgical therapy. The use of corticosteroids will likely shrink the tumor and may facilitate excision. However, the primary effect of corticosteroids is most likely to be anti-inflammatory, rather than cytotoxic. This may result in a decrease in tumor size, but the continued presence of tumor cells in the tumor periphery. This approach is warranted if the goal is cytoreduction and primary closure, followed by radiation therapy. It may, however, give the surgeon a false sense of security if a curative intent excision is part of the treatment plan. Chemotherapy such as vinblastine or palladia, may be effective as a tool to downstage mast cell tumors prior to wide surgical excision because of their cytotoxic effects. However, this remains to be reported in the veterinary literature. In general, if a mast cell can be removed with clean margins with a wide excision, it is recommended by the author to excise the tumor without downstaging first, with downstaging reserved for cases where a curative excision is not possible or not possible without unacceptable morbidity to the patient. In these cases, adjuvant radiation therapy may also be a necessary part of treatment.  [...]