‘Atypical’ Blue Nevus – a Benign Variant of Cellular Blue Nevus

Abstract

Three cases of ‘atypical’ blue nevus presented almost identical histological findings differing from both benign cellular blue nevus and malignant blue nevus or malignant melanoma, and suggesting malignancy. Long-term follow-up – in one case 19 years – indicates that this pigmented tumor is a benign variant of blue nevus.

Oral Atypical Cellular Blue Nevus: An Infiltrative Melanocytic Proliferation

“…Lastly, inflammation is frequently noted at the periphery of melanomas but is typically absent in CBN [2]. Inflammation in MBN is highly variable [9,11] and in the 14 well-documented cases of ACBN it was seen in 10 (71 %), with 6 showing only a ''mild'' reaction [16,17,27]. Our case lacked necrosis or a significant inflammatory response, both indicating a less aggressive process.…”

“…The CBN occur on the buttocks/lumbosacral region followed by the scalp, face and hand [2,23]. ACBN cases similarly affect the buttocks, scalp and the extremities [16,17,27] while MBN have somewhat greater propensity to affect the scalp [11]. Women are affected more often than men for CBN and ACBN whereas MBN affects men more frequently [1,17] but these differences are modest.…”

“…Specifically, cellular pleomorphism, numerous bizarre and heavily pigmented multinucleated cells and giant cells [16,27] as well as atypical and mostly nonpigmented cells with hyperchromatic nuclei were reported [27]. Only a ''few mitoses'' were reported in 1 of the 5 cases from these 2 studies.…”

“…Cases of CBN rarely recur and do not metastasize [2] while MBN often recur, metastasize and frequently lead to death [9][10][11]. The intermediate designation of ACBN has drawn some criticism [15] due to the fact that, of the well-characterized cases, only one has recurred and none have metastasized [16,17,27]. The follow-up period varied tremendously in these cases from 12 to 228 months with an average of nearly 59 months.…”

“…When unquestionably malignant features such as widespread necrosis, mitotic activity, atypical mitoses and marked cytologic atypia are juxtaposed next to an otherwise bland CBN, the diagnosis is straightforward. However, multiple reports in recent decades of tumors with features intermediate between CBN and MBN prompted the controversial [15] designation of ''atypical blue nevus'' or ''atypical cellular blue nevus'' (ACBN) [16,17]. While similar clinically and apparently biologically to CBN [17], discrete histologic criteria for ACBN are currently under debate even among expert dermatopathologists [18][19][20][21][22].…”