San Diego – The way Benjamin Kelley, MD, sees it,
Doug Brunk/MDedge News
Dr. Benjamin Kelley
“There’s a confusion in the terminology, a term the late A. Bernard Ackerman, MD, called ‘patho-babel,’ ” Dr. Kelley, a Mohs micrographic surgeon and dermatopathologist in La Jolla, Calif., said at the annual Cutaneous Malignancy Update. “The idea of DN was originally used to describe a clinical melanoma syndrome. Now we use it for individual lesions, not just clinically but histologically. Some dermatologists refer to DN as ‘pre-melanoma,’ which is a negative framing,” he noted.
“We also refer to common nevi as ‘benign,’ which implies that DN are not benign,” he added. “The good news is that regardless of what they are called, the histologic criteria is generally agreed upon. The names can be used interchangeably.”
The bad news, he continued, is that there is less-than-perfect interobserver variability for grading DN lesions and significant variability in the treatment recommendations that pathologists give to clinicians. In one study, a group of pathology experts was asked to review 48 photomicrographs of melanocytic lesions and provide their diagnosis and treatment recommendations based on the Melanocytic Pathology Assessment Tool and Hierarchy for Diagnosis scheme. For one, which showed a broad lesion with irregular epidermal thinning and thickening, the diagnoses ranged from solar lentigo to melanoma in situ. Treatment recommendations ranged from no treatment to re-excise with appropriate margins.
“This is an extreme example, but it shows you how difficult [establishing a diagnosis] can be,” Dr. Kelley said.
In a more recent study, researchers analyzed interobserver reproducibility in grading 179 DN cases among three observers who applied the 2018 World Health Organization grading criteria. The observers showed moderate to good agreement for most of the architectural features, except for criteria regarding focal continuous basal proliferation of melanocytes, density of non-nested junctional melanocytes, and presence of dyscohesive nests of intraepidermal melanocytes, whereas fair agreement was achieved for the cytological criteria. “So, it sounds to me like there was not a whole lot of agreement,” Dr. Kelley said.
An earlier single-center study titled “Clinicians Are From Mars and Pathologists Are From Venus” found that surgeons misunderstood the pathologist’s report 30% of the time.
In Dr. Kelly’s opinion, management of DNs will be successful if clinicians have a good working relationship with their dermatopathologists, if they biopsy to ensure an adequate, representative specimen, and if that they know what the terminology on the pathology report means and what actions to take. “The biopsy method matters,” he emphasized.
In a 14-year follow-up survey, investigators assessed DN management trends among 703 U.S. dermatologists. One key finding was that 69% of dermatologists in 2015 performed total removals when biopsying DN to achieve clear margins, compared with 86% in 2001.
A subsequent survey of 213 New England–based dermatologists found that the degree of clinical suspicion for melanoma was important in DN biopsy technique, with more respondents favoring shave biopsies for lesions with low suspicion and full-thickness biopsies for highly suspicious lesions.
“Misdiagnosis is more common for melanomas that have been assessed with punch and shave biopsies than with an excisional biopsy,” Dr. Kelley said. “I’m not too much of a stickler. I don’t require everyone to send me a giant excision, but I do want a representative sample.”
What about re-excision of DN considered to be mild or moderate? In 2015, members of the Pigmented Lesion Subcommittee of the Melanoma Prevention Working Group published a consensus statement on DN management recommendations for clinically atypical nevi/DN based on a review of published evidence. The subcommittee members concluded that mildly and moderately DN with clear margins do not need to be re-excised, and that mildly DN biopsied with positive histologic margins without clinical residual pigmentation may be safely observed rather than re-excised.
For moderately DN with positive histologic margins without clinically apparent residual pigmentation, the subcommittee members concluded that observation may be reasonable.
In his own informal analysis, Dr. Kelley compiled data from published studies he could find on DN management and divided them into two groups: the observation group, in which researchers from eight studies biopsied the DN lesion and watched the patients over time to see what happened, and the re-excision group, in which researchers from seven studies biopsied the DN lesion and subsequently re-excised it. There were about 1,500 patients in both groups. No deaths occurred in either group, he said, but 15 patients in the re-excision group developed a melanoma at the site of the original biopsy (1%), compared with 7 in the observation group (0.5%).
Six of seven melanomas in the observation group came from one article conducted at a VA clinic. In the study, 6 of 304 observed DN subsequently developed melanoma at the site of the lesion. “However, five of six that developed melanoma had an original biopsy that was a partial biopsy with grossly positive margins; I think that’s where the problem lies,” Dr. Kelley said at the meeting, which was hosted by Scripps MD Anderson Cancer Center. “All five grew lentigo maligna type melanoma, which we know can extend multiple millimeters beyond the clinically apparent lesion.”
The findings support mounting evidence that re-excising mild and moderate DN, regardless of border involvement, may not be necessary. “Currently, most clinicians still re-excise moderate and severe DN involving margins, especially if there is residual pigment,” Dr. Kelley said. “Most re-excise severe DN regardless of margin involvement, but beware if your biopsy was a partial sample of a larger lesion.”
He acknowledged limitations to pathologic studies of DN, including the potential for diagnostic uncertainty. “That doesn’t necessarily mean that the pathologist got the diagnosis wrong. It could be, what is the risk that the portion of tissue not visualized contains melanoma? If you give me a 5 mm sample of a DN, and I cut it into 4-micrometer sections, I’m only looking at less than 1% of the actual nevus. That’s compounded if the pathologist only receives a partial sample.”
Dr. Kelley reported having no relevant disclosures.