Safety margins are considered to be the required distance from a given tumor that will theoretically result in complete excision of the tumor; safety margins are used in surgical planning.1 These margins usually are derived from studies conducted to evaluate outcome related to histologic margins or outcome, compared with the macroscopic safety margins used during surgery. The concept of a safety margin has many confounding factors; however, understanding the relationship of these planned surgical margins to histologically determined margins is necessary to better interpret outcomes related to these measures.1–3
Histopathologic margins are often the standard used to measure success of surgical resection and have been associated with the prognosis for a patient.3,4 The working definition of a histopathologic margin or histopathologic safety margin is the distance from the cut edge of the surgical sample to the closest identifiable tumor cell.5,6 Although histopathologic margins are often considered a defined and objective measure, there are many sources of error and subjectivity that can add uncertainty to interpretation of the results. For cutaneous tumors, separation of deeper anatomic layers from the skin, type of tumor, surgical method, postoperative handling, method of histologic sectioning, and various patient factors can all influence measurements of histopathologic margins.1,2,6–8 Also, the phenomenon of shrinkage (ie, change in sample size between presurgical measurements and posthistologic processing) has been described,8–11 and this phenomenon further complicates interpretation of histopathologic margins in relation to planned surgical margins.
Most of the studies conducted to evaluate skin shrinkage after surgical excision have been performed on samples obtained from humans. Factors reported to influence the amount of skin shrinkage include patient age, location of the tumor, inherent elasticity of the skin in that patient, and presence of scar tissue.10 However, there have been conflicting results that indicate age, sex, and skin lesion type (benign vs malignant) do not affect shrinkage.9 It was once commonly believed that histologic processing, specifically formalin fixation, may affect skin shrinkage. However, studies in human9,10 and veterinary12 medicine have found that formalin fixation has little or no effect on change in sample size.
Shrinkage of samples of clinically normal skin of dogs has been evaluated in 2 studies.3,12 Investigators of the earlier study3 found that the degree of shrinkage is dependent on location and reported that inclusion of a muscle layer but not a fascial plane may decrease the amount of shrinkage. Investigators of the latter study12 evaluated sample size, location, and tension lines; however, in contrast to the earlier study, they did not find that location affected skin shrinkage. Although the earlier study included histologic processing, effects of processing were not assessed independent from effects of formalin fixation. The effect of histologic processing on size of skin samples was not assessed in either of those studies.
The purpose of the study reported here was to examine the relationship between planned surgical and histopathologic margins by evaluating factors (eg, size of skin sample, anatomic location, and histologic processing) that may affect shrinkage. We hypothesized that the degree of shrinkage of histologically processed clinically normal skin samples differs on the basis of sample size and location and that shrinkage occurs following histologic processing, but to a lesser degree, than the shrinkage that occurs between excision and formalin fixation.
This manuscript represents a portion of a thesis submitted by Dr. Reagan to the University of Illinois Department of Clinical Sciences as partial fulfillment of the requirements for a Master of Science degree.
No third-party funding or support was received in connection with this study or the writing or publication of the manuscript. The authors declare that there were no conflicts of interest.
Presented as a poster at the Veterinary Cancer Society Conference, St Louis, October 2014.
Davidson marking system, Bradley Products Inc, Bloomington, Minn.
ImageJ, version 1.48, 1US National Institutes of Health. Bethesda, Md: Available at: imagej.nih.gov/ij/. Accessed Apr 30, 2014.
Microsoft Excel for Mac 2011, version 14.4.4, Microsoft Corp, Redmond, Wash.
SAS software, version 9.3, SAS Institute Inc, Cary, NC.
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