8723/0 Halo nevus


Synonyms

Regressing nevus

Definitions

Skin
ICD-O-3 topography code: C44

A halo nevus is a small benign pigmented lesion surrounded by a characteristic symmetrical area of depigmentation (the "halo"). A dense lymphocytic infiltrate extends among the lesional nevus cells. An early halo nevus presents as a symmetrical, circumscribed, usually papular lesion, generally <4 mm in diameter, and is composed of nevus cells located in papillary dermis and epidermis. Approximately 50% of cases show mild to moderate cytologic atypia. The epidermis may be hyperkeratotic with follicular plugging. In the course of the ensuing weeks or months, the dermal nevus cells disappear, followed by the disappearance of the inflammatory cells.
The inflammatory infiltrate consists mainly of T lymphocytes (APCs and CD8+ cells), which implicates cytotoxic mechanisms in the destruction of nevus cells. T cell clonal expansion and anti-nevic IgM production in affected individuals also are consisent with the idea that halo nevi represent immunological rejection of a nevus.
Halo nevi are most common in teenagers and young adults1
 
LeBoit PE, Burg G, Weedon D, Sarasin A (Eds.)
World Health Organization Classification of Tumours. Pathology and Genetics of Skin Tumours
3rd Edition
IARC Press: Lyon 2005



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