Mohs micrographic surgery (MMS) is most commonly used for the surgical management of squamous cell carcinomas (SCCs) and basal cell carcinomas (BCCs) in high-risk locations. The ability for 100% margin evaluation with MMS also has shown lower recurrence rates compared with wide local excision for less common and/or more aggressive tumors. However, there is a lack of standardization on initial and subsequent margin size when treating these less common skin tumors, such as dermatofibrosarcoma protuberans (DFSP), atypical fibroxanthoma (AFX), and sebaceous carcinoma.
Because Mohs surgeons must balance normal tissue preservation with the importance of tumor clearance in the context of comprehensive margin control, we aimed to assess the practice patterns of Mohs surgeons regarding margin size for these unique tumors. The average margin size for each Mohs layer has been reported to be 1 to 3 mm for BCC compared with 3 to 6 mm or larger for other skin cancers, such as melanoma in situ (MIS).1-3 We hypothesized that the initial margin size would vary among surgeons and likely be greater for more aggressive and rarer malignancies as well as for lesions on the trunk and extremities.
A descriptive survey was created using SurveyMonkey and distributed to members of the American College of Mohs Surgery (ACMS). Survey participants and their responses were anonymous. Demographic information on survey participants was collected in addition to initial and subsequent MMS margin size for DFSP, AFX, MIS, invasive melanoma, sebaceous carcinoma, microcystic adnexal carcinoma (MAC), poorly differentiated SCC, Merkel cell carcinoma, extramammary Paget disease, leiomyosarcoma, and endocrine mucin-producing sweat gland carcinoma. Survey participants were asked to choose from a range of margin sizes: 1 to 3 mm, 4 to 6 mm, 7 to 9 mm, and greater than 9 mm. This study was approved by the University of Texas Southwest Medical Center (Dallas, Texas) institutional review board.
Eighty-seven respondents from the ACMS listserve completed the survey (response rate <10%). Of these, 58 respondents (66.7%) reported practicing for more than 5 years, and 58 (66.7%) were male. Practice setting was primarily private/community (71.3% [62/87]), and survey respondents were located across the United States. More than 50% of survey respondents treated the following tumors on the head and neck in their respective practices: DFSP (80.9% [55/68]), AFX (95.6% [65/68]), MIS (67.7% [46/68]), sebaceous carcinoma (92.7% [63/68]), MAC (83.8% [57/68]), poorly differentiated SCC (97.1% [66/68]), and endocrine mucin-producing sweat gland carcinoma (51.5% [35/68]). More than 50% of survey respondents treated the following tumors on the trunk and extremities: DFSP (90.3% [47/52]), AFX (86.4% [45/52]), MIS (55.8% [29/52]), sebaceous carcinoma (80.8% [42/52]), MAC (73.1% [38/52]), poorly differentiated SCC (94.2% [49/52]), and extramammary Paget disease (53.9% [28/52]). Invasive melanoma, Merkel cell carcinoma, and leiomyosarcoma were overall less commonly treated.
In general, respondent Mohs surgeons were more likely to take larger initial and subsequent margins for tumors treated on the trunk and extremities compared with the head and neck (Table). In addition, initial margin size often was larger than the 1- to 3-mm margin commonly used in Mohs surgery for BCCs and less aggressive SCCs (Table). A larger initial margin size (>9 mm) and subsequent margin size (4–6 mm) was more commonly reported for certain tumors known to be more aggressive and/or have extensive subclinical extension, such as DFSP and invasive melanoma. Of note, most respondents performed 4- to 6-mm margins (37/67 [55.2%]) for poorly differentiated SCC. Overall, there was a high range of margin size variability among Mohs surgeons for these unique and/or more aggressive skin tumors.
Given that no guidelines exist on margins with MMS for less commonly treated skin tumors, this study helps give Mohs surgeons perspective on current practice patterns for both initial and subsequent Mohs margin sizes. High margin-size variability among Mohs surgeons is expected, as surgeons also need to account for high-risk features of the tumor or specific locations where tissue sparing is critical. Overall, Mohs surgeons are more likely to take larger initial margins for these less common skin tumors compared with BCCs or SCCs. Initial margin size was consistently larger on the trunk and extremities where tissue sparing often is less critical.
Our survey was limited by a small sample size and incomplete response of the ACMS membership. In addition, most respondents practiced in a private/community setting, which may have led to bias, as academic centers may manage rare malignancies more commonly and/or have increased access to immunostains and multispecialty care. Future registries for rare skin malignancies will hopefully be developed that will allow for further consensus on standardized margins. Additional studies on the average number of stages required to clear these less common tumors also are warranted.