Читать книгу Veterinary Surgical Oncology - Группа авторов - Страница 32

The quality of the margin may be more influential than the quantity. Tissue barriers such as muscle, fascia, joint capsule, cartilage, and bone are inherently resistant to tumor penetration. Most solid tumors expand within their tissue of origin initially and grow along lines of least resistance. Surgical oncologists understand that including a tissue barrier beyond where the tumor is attached will trump a larger tissue margin in the absence of that barrier in terms of the likelihood of obtaining complete margins. However, fascia, often favored as a good tissue barrier and easily identifiable to the surgeon, is frequently difficult to discern as a distinct structure on histological sections. This creates difficulty in margin interpretation especially when minimum distances between the fascial plane used as a surgical margin and the nearest tumor cell exist. Is the patient at higher risk for recurrence with a 2‐cm histologic margin of normal fat or a 2‐mm histologic margin of normal tissue that includes a defined fascial layer (per surgeon reporting)?

Human medical evidence has suggested that qualifying the peripheral growth pattern of sarcomas as either “pushing” (no infiltration into surrounding tissue beyond the pseudocapsule) or “infiltrative” (tumor pseudocapsule poorly defined or satellite nodules present) was predictive of local recurrence (Engellau et al. 2005, 2007). The “pushing” contour was seen most commonly in low‐grade sarcomas, but a significant percentage of high‐grade sarcomas also displayed this characteristic (Engellau et al. 2007). High‐grade tumors with a “pushing” growth pattern had significantly fewer local recurrences than high‐grade tumors with “infiltrative” growth patterns (Engellau et al. 2007; Lintz et al. 2012). It is therefore possible that in even high‐grade sarcomas, a pushing pattern of peripheral growth may allow a narrower resection than a tumor with an infiltrative contour. These features (pushing or infiltrative) can be seen on MRI (Iwata et al. 2014; Nakamura et al. 2017), making it conceptually possible to plan resection margins preoperatively based on tumor contour features; however, this approach has not been studied extensively in human medicine or at all in veterinary medicine.

Compartmental tumor excision has been proposed by Enneking and others as a means to diminish the risk of local recurrence in musculoskeletal sarcomas. In compartmental excision, an entire compartment of tissue is removed, for example, an entire muscle or muscle group, as opposed to circumferentially resecting en bloc. Proponents argue that wide local excision, involving an arbitrary measure of a normal tissue “cuff,” risks leaving satellite nodules beyond the resected plane, especially in high‐grade, infiltrative tumors. Indeed, compartmental tumor excision has been shown to reduce recurrences in some tumor types and may be worth considering adopting in veterinary surgical oncology.

Currently, the best‐known predictors for local recurrence of solid tumors are histologic grade and completeness of excision. These features are typically assessed after resection, although grade may be determined prior to resection if the tumor is biopsied and sufficient tissue can be evaluated. Newer technologies such as genome sequencing and proteome analysis are designed to probe deeper into the biological aggressiveness of an individual tumor. Utilization of these methods may provide more specific information, can be acquired prior to surgery, and will provide information from both the tumor and the surrounding microenvironment. The microenvironment/tumor stroma is becoming a featured player in the understanding of tumor biology, as scientists begin to understand the importance of a permissive microenvironment and its role in invasion and metastasis. These datasets may ultimately provide the most accurate assessment of biologic behavior and subsequently assist the surgeon in personalized surgical planning. These analyses may prove to be far more predictive of both local recurrence and metastatic potential than histologic grade.

Given the myriad factors that influence assessment and reporting of surgical margins, it stands to reason that surgical oncologists need to collaborate with pathologists to standardize margin reporting and continue to assess the most predictive prognostic factors within each specific tumor type. It may be that the distance method is better for predicting recurrence in one type or grade of tumor, whereas in a different tumor type, the qualitative method may be most predictive. It is imperative that surgeons understand the limits and advantages of various methods of tissue sectioning and margin interpretation, and continue to develop new means of assessing biological aggressiveness. A one‐size‐fits‐all approach is no longer the best medicine.