Melan-a-positive "pseudomelanocytic nests": a pitfall in the histopathologic and immunohistochemical diagnosis of pigmented lesions on sun-damaged skin

Beltraminelli, Helmut; Shabrawi-Caelen, Laila El; Kerl, Helmut; Cerroni, Lorenzo (2009). Melan-a-positive "pseudomelanocytic nests": a pitfall in the histopathologic and immunohistochemical diagnosis of pigmented lesions on sun-damaged skin. American journal of dermatopathology, 31(3), pp. 305-8. Hagerstown, Md.: Lippincott Williams & Wilkins 10.1097/DAD.0b013e31819d3769

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We encountered recently 3 cases with a histopathologic diagnosis of melanoma in situ on sun-damaged skin (male = 2, female = 1; median age: 59 years; range: 52-60 years). The diagnosis was based mainly on the finding of actinic elastosis in the dermis and increased number of melanocytes in the epidermis and was confirmed by strong positivity for Melan-A in single cells and in small nests ("pseudomelanocytic nests"), located at the dermoepidermal junction. Indeed, examination of slides stained with hematoxylin and eosin revealed the presence of marked hyperpigmentation and small nests of partially pigmented cells at the dermoepidermal junction, positive for Melan-A. The histologic and especially the immunohistochemical features were indistinguishable from those of melanoma in situ on chronic sun-damaged skin. In addition, a variably dense lichenoid inflammation was present. Clinicopathologic correlation, however, showed, in all patients, the presence of a lichenoid dermatitis (phototoxic reaction, 1 case; lichen planus pigmentosus, 1 case; and pigmented lichenoid keratosis, 1 case). Our cases clearly show the histopathologic pitfalls represented by lichenoid reactions on chronic sun-damaged skin. Immunohistochemical investigations, especially if performed with Melan-A alone, may lead to confusing and potentially disastrous results. The unexpected staining pattern of Melan-A in cases like ours raises concern about the utility of this antibody in the setting of a lichenoid tissue reaction on chronic sun-damaged skin. It should be underlined that pigmented lesions represent a paradigmatic example of how immunohistochemical results should be interpreted carefully and always in conjunction with histologic and clinical features.

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Journal Article (Further Contribution)


04 Faculty of Medicine > Department of Dermatology, Urology, Rheumatology, Nephrology, Osteoporosis (DURN) > Clinic of Dermatology

UniBE Contributor:

Beltraminelli, Helmut




Lippincott Williams & Wilkins




Factscience Import

Date Deposited:

04 Oct 2013 15:12

Last Modified:

04 May 2014 23:23

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URI: (FactScience: 196429)

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