5mm margin ‘enough’ for small melanoma in situ

Skin cancers

By Geir O'Rourke

1 Jul 2024

The debate over the minimum appropriate margins when excising melanoma in situ has taken another turn, after an Australian study found low recurrence rates with 5 mm margins on lower-risk sites.

While mostly limited to smaller lesions under 10mm in width, the data indicate that conservative 5 mm margins are likely to be suitable in these ‘bread and butter’ cases, the investigators say.

Their case series analysis studied all melanoma in situ (MIS) lesions from a private Brisbane dermatology clinic between 2011 and 2018, including 315 lesions with a documented 5 mm excisional margin and more than five years of site-specific follow-up after wide local excision.

Of these, a total of 348 (99.1%) did not have clinical recurrence, the authors reported in JAMA Dermatology (link here). The other three lesions did experience local recurrence, but with no metastatic spread, according to the team.

“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><10mm) may reduce morbidity and cost associated with treatment without compromising patient outcomes in a select population of lesions,” the authors wrote.

At less than 1%, the rate of recurrence was broadly in line with that found for MIS in the Mohs micrographic surgery studies, which had reported rats between 0.26% and 1.1% with excisional margins between 6 and 12mm required, they said.

Led by senior author Professor James Muir FACD, director of dermatology at Mater Hospital, Brisbane, the investigators noted the current literature supported substantially wider excision margins for larger lesions, and those in higher risk regions such as the head and neck.

“Therefore, the result of this study may not generalize to larger or more ill-defined lesions,” they wrote.

“Although all MIS lesions had formally documented 5-mm excisional margin WLE, we acknowledge that determining the extent of an MIS lesion may differ between operators and the final margin of excision may vary for that reason.”

Finally, six lesions (1.7%) required repeat surgery in the study, illustrating that a smaller margin may infer a higher risk of positive margins requiring further excisions, the authors said.

Superficial spreading melanoma was the most common subtype diagnosed in the case series (177 lesions), followed by lentigo maligna (107 lesions) and lentiginous MIS (67 lesions).

The trunk was the most common location, followed by upper limb and lower limb, while most of the lesions were small, with 274 having a length less than 10mm and 312 having a width less than 10mm. 

Data show some margins can be reduced: expert

In a linked editorial, leading US dermatologist Professor John Zitelli said the findings indicated there was a place for conservative margins, particularly for very small, low-risk lesions of MIS with a median diameter of 5 mm on the trunk and extremities (link here).

Nevertheless, he stressed he could only recommend 5mm excision margin after excisional biopsy with 2-3mm margins and in this subgroup of small low-risk lesions.

Professor Zitelli, a senior academic at the University of Pittsburgh who himself trained in Mohs micrographic surgery under the direction of Dr Frederic Mohs, noted that recommendations for treating MIS were not based on RCTs and had always been controversial.

He said initial recommendations of a 5mm surgical margin for MIS were suggested by the US National Institutes of Health, based on dermatologist’ experience rather than scientific evidence, but this became the recommended excision margin adopted by many national and international groups writing clinical guidelines.

However, Mohs surgeons had taken a different view, supported by studies showing that MIS often extended beyond a 5mm clinical margin, and wider margins were necessary to avoid local recurrence and tumour progression, Professor Zitelli said.

“Today, most clinical guidelines recommend a range of margins of 0.5-1cm for all MIS, noting that the goal of excision is negative histologic margins,” he wrote.

He added: “To incorporate the findings of this study into clinical practice, the preplanned surgical margin of 7-8 mm can be reduced to 5 mm if it is known that the biopsy included the same 2-3 mm of normal skin, as done in this study.”

“However, this margin cannot be extrapolated to all lesions of MIS. Larger (>1 cm), low-risk lesions on the trunk and extremities may require 1-cm margins and still offer local recurrence rates of about 2%.”

“However, for MIS lesions that are at high risk for recurrence because of poorly defined margins, a recurrent nature, or being amelanotic in colour, of a larger size, or located on the head, neck, hands, feet, or genitalia, Mohs surgery with immunostaining of the margins can potentially minimize recurrence and reduce morbidity and mortality of MIS.”

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