Table 3 Histopathological and immunohistochemical features of cutaneous diseases of uncertain biological behaviour that can mimic melanoma
Intraepidermal mimicHistopathological featuresImmunohistochemical features
Langerhans cell histiocytosis*

  • Aggregates of Langerhans cells in the epidermis characterised by abundant blue-grey cytoplasm, indented oval nuclei with a central groove

  • Little or no cytological atypia

  • Dermal infiltrate of Langerhans cells that form sheets with accentuation below the epidermis

  • Absence of melanin pigment, and presence of eosinophils

  • S-100 (+), CD1a (+)

  • HMB 45 (−), Mart 1/Melan A (−)

  • *The ultrastructural hallmark of Langerhans cells is the rod or rocket shaped granules (Birbeck granules, Langerhans cell granules), which may be needed to establish the diagnosis of Langerhans cell histiocytosis.