Immunohistochemical Staining with Melan-A of Uninvolved Sun-damaged Skin Shows Features Characteristic of Lentigo Maligna

Background: The greater density and unusual patterning of melanocytes in chronically sun-exposed skin complicates interpretation of intraoperative Melan-A immunohistochemical stained margins during margin-controlled surgery for lentigo maligna (LM) and lentigo maligna melanoma (LMM).

Objective: To identify the immunohistochemical similarities and differences in melanocyte distribution between LM and LMM and chronically sun-exposed skin.

Methods: Retrospective review of Melan-A-stained original biopsy specimens of LM and LMM and uninvolved sun-damaged skin (negative controls), from 70 LM and LMM cases from the University of Utah in 2008.

Results: Histologic features commonly associated with LM were common in negative controls from chronically sun-exposed skin. Melanocyte confluence (27/70, 39%), stacking (34/70, 49%), theque formation (9/70, 13%), adnexal extension (59/68, 87%), and suprabasilar scatter (23/70, 33%) were observed in the negative controls from sun-damaged skin. Such features were present nearly uniformly in the LM and LMM specimens. Epidermal melanocyte density in LM and LMM differed significantly from that in negative controls (82.7 ± 29.3 and 25.6 ± 9.3 per × 400 field, respectively; p<.001).

Conclusion: Epidermal melanocytic features often ascribed to LM, such as melanocyte confluence, stacking, theque formation, adnexal extension, and suprabasilar scatter, are frequently observed in chronically sun-exposed Caucasian skin and may lead to overestimation of surgical margins.