Conservative excisional margin for small MIS tied to low recurrence

For small-sized melanoma in situ (MIS; <10 mm) on low-risk body sites, wide local excision (WLE) using a 5-mm margin was associated with a low rate of recurrence, a retrospective case series study has shown.

“[For MIS,] excision remains the gold standard treatment. This study shows that excision using 5-mm margins of MIS of smaller size on low-risk body sites is associated with low recurrence rates and high rates of reported margin clearance after standard histopathologic reporting by pathologists,” said the researchers.

The study included 351 MISs from 292 patients (mean age 60.3 years, 55.5 percent women). Of the lesions, 345 had clear histopathologic margins after initial WLE with 5-mm margin, while six lesions required more than one WLE to achieve adequate histologic margins. None had additional topical imiquimod or radiotherapy as adjuvant therapy. [JAMA Dermatol 2024;160:874-877]

After a median follow-up of 7 years, only three MISs recurred locally within the previous excision scar with no regional or distal metastasis during the duration of the study. This corresponded to 0.9 percent. Almost all lesions (99.1 percent) had no documented recurrence.

Furthermore, all recurrences were re-excised with clear margins, and no further recurrence was reported after at least 5 years of additional follow-up.

Lesion characteristics

The mean dimensions of the diagnosed lesions were 6 × 5 mm. Three-quarters (78.1 percent) of the lesions had a length <10 mm, and 88.9 percent had a width <10 mm.

The most common subtype diagnosed was superficial spreading melanoma (50.4 percent), followed by lentigo maligna (30.5 percent) and lentiginous MIS (19.1 percent). About half (47.9 percent) of the lesions were found in the trunk, while the rest were in the upper (27.4 percent) and lower limbs (16.8 percent).

Seventy percent of the lesions had undergone initial excisional biopsy, while the remaining 30 percent had shave excision.

Reduced morbidity, costs

In the Mohs micrographic surgery studies, the reported rate of recurrence for MIS has been between 0.26 percent and 1.1 percent, with excisional margins between 6 and 12 mm. [JAAD Int 2022;7:169-176; JAMA Dermatol 2017;153:436-441; J Am Acad Dermatol 2005;52:92-100; Dermatol Surg 2000;26:771-784]

“This study demonstrated a comparable 0.9-percent recurrence rate achieved with a conservative 5-mm excisional margin. This shows that using a 5-mm margin for MIS of smaller size (<10 mm) may reduce morbidity and cost associated with treatment without compromising patient outcomes in a selected population of lesions,” the researchers explained.

However, according to the researchers, the six lesions that required repeat surgery implies that a smaller margin may infer a higher risk of positive margins that require further excisions, which has associated cost and logistical burden.

Also, the findings may not be applicable to larger or more ill-defined lesions or those in high-risk areas, as these may require substantially wider excision margins. [J Am Acad Dermatol 2002;47:743-748; Arch Dermatol 2004;140:1087-1092]

“[Nonetheless,] conservative 5-mm excisional margin is likely to be suitable for small MIS on lower-risk body sites,” said the researchers. “Further studies should be done to explore the applicability of simple complete excision in small MIS.”