Читать книгу Veterinary Surgical Oncology - Группа авторов - Страница 29

The evaluation of surgical margins of an excised specimen is an essential component to appropriate care in a cancer patient. A surgical margin denotes a tissue plane established at the time of surgical excision, the tissue beyond which remains in the patient. Excised masses should be submitted in their entirety for evaluation of the completeness of excision. The surgeon should indicate the margins with ink or some other method prior to placing the specimen in formalin to aid the pathologist in identifying the actual surgical margin. Because the larger tumor specimen is trimmed by a technician to fit on a microscope slide, the pathologist may not be oriented as to what represents a surgical margin versus a sectioning “margin.” Tissue ink on the surgical margin allows there to be orientation throughout sectioning. The ink is present throughout the processing of the tumor specimen and is visible on the slide. If tumor cells are seen at the inked margin under the microscope, the surgical margin is by definition “dirty” or incomplete.

There is considerable confusion and controversy surrounding the issue of appropriate surgical margins and clinical decision‐making when histologically incomplete margins are obtained. Prior dogma has suggested that an overly generous margin is likely to be curative. In order to ensure a good oncological outcome, surgical oncologists have been trained to be as aggressive as possible. While it is well‐accepted that aggressive surgical margins tend to lead to better local control, this is not true in every case. Even extensive, complete surgical margins do not always lead to a cure. Local recurrence and/or metastasis may occur despite a histologically complete margin. Mounting evidence in the human sarcoma literature seems to suggest that a planned and executed “widest” surgical margin has not resulted in sufficient improvements in disease‐free intervals to justify the morbidity incurred with such resections. This opinion among human surgeons is confounded by the routine use of adjuvant radiation therapy in traditionally difficult‐to‐resect tumors such as extremity sarcomas. In veterinary medicine, adjuvant radiation therapy may not be available or affordable. As we know from experience and from the veterinary literature, not every patient with a histologically positive margin will experience recurrence. To confound things further, different malignancies and grades of malignancy (mast cell tumor vs. soft tissue sarcoma, low grade vs. high grade) may require specific and separate guidelines for margin planning.

Veterinary surgical oncology has traditionally followed the adage that for most malignant solid tumors, a 2–3 cm surgical margin and an additional tissue plane deep is the desired intraoperative goal to achieve wide excision, and is most likely to result in a histologically clean excision. Nonetheless, many surgical oncologists bend these “rules” based on tumor‐specific evidence in the literature and personal experience. Examples of this include using proportional margins in mast cell tumor resection (Pratschke et al. 2013) or less generous margins for specific anatomic areas, where 2–3 cm could result in undesirable functional morbidity (e.g. head and neck, spinal column). Many, based on experience, feel comfortable with smaller margins in specific tumor types (anal sac tumors, thyroid tumors, low‐grade sarcomas) and in some cases, this is supported in the veterinary literature by findings of no difference in local recurrence between one “width of margin” and a lesser one. However, the minimum safe distance necessary to reduce the chance of local recurrence is currently unknown. Regardless of what is actually performed in the operating room, most of the published literature agrees that a histologic margin free of tumor cells is considered the best predictor of improved local recurrence.