[466] Definition and Categorization of Combined Melanocytic Nevi.

Johanna L Baran, Lyn M Duncan. Massachusetts General Hospital, Boston

Background: “Combined nevus” is a term used to describe tumors composed of two or more distinct populations of melanocytes. While this term has historically been used to describe the combination of blue nevi with common nevi, it has more recently been applied to other combinations of benign melanocytic proliferations. We sought to document the use of this terminology and the incidence and distribution of these tumors to propose consistent diagnostic nomenclature for practical use and comparison.
Design: The electronic records were reviewed for all cases that included both the terms "combined" and "nevus" in the diagnosis field between the years 2000-2010. The cases identified were then examined for diagnosis, presence of atypia, as well as age and sex of the patient.
Results: 514 combined nevi were identified, represented by four histologically distinct diagnostic categories: “common” junctional, dermal, compound or dysplastic nevus combined with 1) blue nevus, 2) Spitz or pigmented spindled cell nevus, 3) deep pigmented nevus (plexiform, deep penetrating, inverted type A), or 4) other combinations with or without a common nevus component. Of these nevi, 18% displayed cytological atypia, observed more often in combined common nevi with Spitz or deep pigmented elements (26/55, 47% and 23/97, 24% respectively) than in combined common and blue nevi (37/337, 11%). There was no difference in age distribution or gender between histological categories or in the banal versus atypical nevi.

Combined nevus histological and clinical distribution

Diagnosis	All cases	Inside cases	Consult cases	Age (mean)	Sex
Combined common and blue	337	321	16	4-86 (47)	179F:158M
Combined common and Spitz	55	50	5	7-76 (35)	34F:21M
Combined common and deep pigmented	97	84	13	4-79 (40)	58F:33M
Other combination	25	21	4	-	-

Conclusions: The term "combined nevus" may be applied to a range of melanocytic proliferations. The most common associations are with blue nevi, nevi with deep dermal pigmentation, and Spitz nevi, in decreasing prevalence. Atypia is more often associated with Spitz and deep pigmented tumors. Gender and age do not correlate with histological categorization or presence of atypia. Given the complicated melanocyte morphology of these unusual and sometimes atypical melanocytic tumors and the possibility of melanoma in the differential diagnosis, it is important to report the specific category of the melanocytic proliferation and the presence or absence of atypia in a consistent manner for adequate clinical follow up of the patient and further comparisons between patient specimens.
Category: Dermatopathology

Tuesday, March 1, 2011 9:30 AM

Poster Session III # 118, Tuesday Morning