Atypical Nevi Are Not All Precancerous

No one wants to miss a melanoma when examining a patient. Since severely atypical nevi and early melanomas may be indistinguishable on clinical exam, no one wants to leave such a lesion unbiopsied. Having said that, it is somewhat of an overdiagnosis to equate lesions that are diagnosed as mildly or moderately atypical by a pathologist as definitely precancerous.

Recent publications have documented that re-excisions of moderately atypical nevi, for example, extremely rarely will demonstrate a melanoma.  In my own experience I have never had a melanoma upon re-excision of a moderately atypical nevus. Most re-excisions show only scar tissue from the original biopsy or, less commonly, small residual atypical nevi.  These articles call for simple close monitoring of patients with the atypical mole syndrome or those with a history of moderately atypical nevi rather than wholesale biopsy of large numbers of benign lesions.

The natural history of the great majority of nevi in patients with the atypical mole syndrome who may have 100s of such nevi is that the lesions mature and fade with time and do not evolve into melanomas.

My experience as originator and director of the melanoma center, and later as director emeritus, at the Washington Hospital Center  in Washington DC from 1996 to 2015 was that we accrued about 2000 melanoma patients and an even greater number of patients without a melanoma history but with on average 100 nevi/patient.  Many patients had 200 or more nevi; one had 1300 such lesions.

We found that upon long-term monitoring of this high-risk group of patients with multiple nevi that 2/3 of the melanoma patients had only one melanoma during the time of our monitoring them.  The other 1/3 had 2 melanomas and only about 50 had more than 2.  We also found that upon analysis of pathology reports, about 2/3 of melanomas arose de novo from previously uninvolved skin and only about 1/3 arose from pre-existing nevi. We concluded that it does not make good medical sense to remove large numbers of nevi in order to attempt to decrease the risk of melanoma formation.

Many of our patients at the melanoma center had a history of multiple biopsies of benign or mildly atypical nevi that left scars that the patients objected to.  Indeed, two patients had histories of 500 biopsies of benign lesions, each at about 50 excisions/year,  prior to entry into our clinic.

Since 1996 we have relied upon dermoscopic evaluation of our patients nevi to determine which lesions to biopsy. The routine use of dermoscopy has increased our diagnostic ability and has reduced the number of unnecessary biopsies.  Since 2015 we have added PLA testing of clinically and dermoscopically atypical lesions to our clinic routine. As such, we are able to diagnose smaller melanomas at an earlier stage. Almost all of the melanomas we have diagnosed since I joined the Dermatologic Surgery Center of Washington in July, 2015 have been small (<6mm) melanomas in situ. Thus, we have found that PLA testing is sensitive and reliable and is a useful adjunct to dermoscopy in increasing the specificity of our biopsies.

Gary L. Peck, MD