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.