Recurrence Rate of Small Melanoma In Situ on Low-Risk Sites Excised With 5-mm Excisional Margin.

Importance: The incidence of melanoma in situ (MIS) has increased significantly over the past decades, and traditional guidelines for treatment of MIS have been excision with a 5-mm clinical margin; however, current Australian and other guidelines now recommend 5- to 10-mm margins. This changed recommendation was largely driven by the outcomes of studies using Mohs micrographic surgery, and recent studies using Mohs micrographic surgery are advocating for even wider excisions up to 18 mm for clearance.

Objective: To assess the rate of recurrence of MIS excised with a 5-mm margin.

Design, setting, and participants: This case series studied all MIS lesions from a single private dermatology clinic between January 1, 2011, and November 30, 2018. The criteria for inclusion were a documented 5-mm excisional margin on operation report and more than 5 years of site-specific follow-up after wide local excision. Lesions were excluded if the excisional margin was more than 5 mm or undocumented, there was less than 5 years of follow-up, or they required more than 1 wide local excision. Data analysis was performed January 30 to February 25, 2024.

Intervention: Wide local excision with 5-mm margin.

Results: A total of 351 MISs were identified from 292 patients (mean [SD] age, 60.3 [11.8] years; 162 females [55.5%]). Superficial spreading melanoma was the most common subtype diagnosed (177 lesions [50.4%]), followed by lentigo maligna (107 lesions [30.5%]) and lentiginous MIS (67 lesions [19.1%]). The trunk was the most common location of lesions (168 lesions [47.9%]), followed by upper limb (96 lesions [27.4%]) and lower limb (59 lesions [16.8%]). Scalp was the least common location (2 lesions [0.6%]). Most of the lesions were small, with 274 lesions (78.1%) having a length less than 10 mm and 312 lesions (88.9%) having a width less than 10 mm. A total of 348 lesions (99.1%) did not have clinical recurrence after excision with a 5-mm clinical margin following then current guidelines. A total of 3 lesions (0.9%) experienced local recurrence with no metastatic spread.

Conclusions and relevance: This case series found that excision with a 5-mm margin for MIS of smaller size (<10 mm) on low-risk body sites had a low rate of recurrence. Conservative 5-mm excisional margin is likely to be suitable for small MIS on lower-risk body sites.