Analysis of heterogeneity of atypia within melanocytic nevi.

BACKGROUND Incisional biopsy of clinically atypical nevi continues to be a common practice. Questions can arise as to the adequacy of these partial biopsies. OBJECTIVE To determine whether incisional (partial) biopsy specimens may be considered representative of the entire lesion, atypical nevi submitted to our dermatopathology laboratory were examined for the presence or absence of heterogeneity of atypia within the individual nevi. DESIGN The study included 250 histologically atypical nevi that were selected consecutively from pigmented lesions that were submitted to our dermatopathology laboratory by community and academic dermatologists for histopathologic analysis. Also, 23 moderately to severely atypical and 25 severely atypical nevi from consecutive submissions were added for statistical reasons. Lesions with both clear and involved margins were used. Lesions were considered homogeneous if the atypia involved the entire lesion or heterogeneous if either the atypia was focal or if different degrees of atypia occurred within the same lesion. Atypia was defined by the usual parameters of architectural and cytologic atypia and host response. Also, the degree of atypia in relationship to heterogeneity and to patient age was determined. SETTING The Dermatopathology Laboratory, University of California, Irvine. MAIN OUTCOME MEASURES Outcome measures included the percentage of nevi exhibiting heterogeneity of atypia, heterogeneity of atypia in relation to patient age, degree of atypia in relation to patient age, and degree of atypia in relation to the presence of heterogeneity of atypia. RESULTS Of the 298 nevi examined, 107 (35.9%) were heterogeneous in atypia and 191 (64.1%) were homogeneous in atypia. There was no significant difference in age between patients with heterogeneous lesions and those with homogeneous lesions. There was a statistically significant correlation between the degree of atypia and patient age. The average age of patients with a lesser degree of atypia was 36.9 years, while the average age of patients with a greater degree of atypia was 44.8 years (P<.005). There was no significant correlation between degree of atypia and heterogeneity of atypia (correlation coefficient, 0.1). CONCLUSIONS A clinically significant proportion of atypical nevi exhibited heterogeneity of atypia. Also, there was a significant relationship between the degree of atypia and increasing age (P<.005). Therefore, if a clinically atypical nevus warrants a biopsy, these results give additional support for complete excisional biopsy (which can include shave or punch) to assure adequate histopathologic sampling of the lesion.