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Wide local excision with a 5-mm margin for smaller melanomas in situ (MISs) may be appropriate for sites at low risk of recurrence, Australian researchers suggested, despite recent guidelines recommending margins of up to 1 cm.

Their retrospective case series of small MISs (6 × 5 mm on average) excised with a 5-mm margin showed that 99.1% had no clinical recurrence after at least 5 years of follow-up. The three lesions that did recur were all local recurrences and were re-excised with clear margins, reported Cong Sun, MD, of Mater Hospital Brisbane Raymond Terrace in South Brisbane, and colleagues.

Of note, most of the lesions (71%) had undergone an initial excisional biopsy with a 2- to 3-mm margin, while the remaining underwent shave biopsy, with the goal being removal of the entire lesion, according to the finding in .

The recurrence rate of 0.9% with no regional or distal metastasis is comparable to that reported with Mohs micrographic surgery using excisional margins between 6-12 mm (0.26-1.1%), the researchers said.

"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," wrote Sun and co-authors. "As mortality from MIS is low and most recurrence is in the form of in situ disease, increased margins can only be justified if they significantly reduce the need for further excisions from margin involvement or recurrence."

But in an , John Zitelli, MD, of the University of Pittsburgh School of Medicine, cautioned that clinicians should not generalize from the study "that a 5-mm margin is adequate for all subgroups of MIS."

For instance, given the use of an initial 2- to 3-mm biopsy margin in the study, "a minimum surgical margin of 7 to 8 mm would be required to achieve a similar true negative excision margin," he said.

Margins of 5-mm for smaller MISs were first recommended starting in the early 1990s based on expert experience rather than randomized trial data, Zitelli explained, but the "" with Mohs surgery has suggested that larger margins achieve negative histologic margins in 97% of real-world MISs. Today, most guidelines recommend margins of 5 mm to 10 mm.

He noted that most patients in the series from Sun's team had small MISs of the trunk or extremities and that the analysis excluded lesions requiring two wide local excisions, likely reflecting the patients with more difficult tumors.

The study "documents that a 5-mm excision margin after excisional biopsy with 2- to 3-mm margins may be effective for very small, low-risk lesions of MIS with a median diameter of 5 mm on the trunk and extremities, with a low local recurrence rate," said Zitelli.

"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%," he continued. "For MIS lesions that are at high risk for recurrence because of poorly defined margins, a recurrent nature, or being amelanotic in color, 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."

The case series from Sun and colleagues examined 351 small MISs from 292 patients (mean 60 years; 56% female) treated with 5-mm wide local excision at a single private dermatology clinic in Australia from January 2011 to November 2018.

Patients needed to have 5 years of follow-up and lesions were excluded if they had initially required more than one wide local excision. Most of the excisions were performed by a general practitioner (63%), with the rest done by a dermatologist.

More than three-fourths (78%) of the lesions were smaller than 10 mm in length and 89% were smaller than 10 mm in width (median length 6 mm, range 2-21 mm; median width 5 mm, range 2-14 mm).

Superficial spreading was the most common MIS subtype (50.4%), followed by lentigo maligna (31%) and lentiginous MIS (19%). Most lesions were located on the trunk (48%) or extremities (upper limb, 27%; lower limb, 17%), with 7% located on the neck or face and 0.6% on the scalp.

Six lesions (1.7%) required a second wide local excision "to achieve adequate histologic margins," said Sun and co-authors, but no patients required adjuvant imiquimod or radiotherapy following excision.

Beyond the single-center design and retrospective nature of the study, other limitations cited by the authors included the predominantly small lesion sizes and that biopsy margin pattern for pigmented lesions may not be the same in Australia as in the U.S.

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