Table 2 Intradermal mimics of uncertain biological behaviour

Lesion	Clinical features	Histology	Immunohistochemistry
Primitive non-neural granular cell tumour	Young to middle-aged adults	Cells with prominent granular cytoplasm	(+) Vimentin
	Female predominance	Nuclei with prominent eosinophilic nucleoli	(+) CD10
		Nuclear pleomorphism	(+) PGP 9.5
		Mild mitotic activity	(+) NKI-C3
			(+) CD 68
			(−) S-100
			(−) HMB-45
			(−) CD34
			(−) Desmin
			(−) SMA
			(−) Mart1/MelanA
Langerhans cell histiocytosis*	Scaly, crusted papules or plaques	Aggregates of Langerhans cells in the epidermis characterised by abundant blue–grey cytoplasm, indented oval nuclei with a central groove	(+) S-100,
	Affects children mainly	Little or no cytological atypia	(+) CD1a
		Dermal infiltrate of Langerhans cells that form sheets with accentuation below the epidermis; absence of melanin pigment, and presence of eosinophils	(+) Langerin (CD207)
			(−) HMB-45
			Mart 1/Melan A (−)
Inflammatory myofibroblastic tumour of the skin	Solitary firm papules and nodules	Bland spindle cells in dermis and subcutaneous fat	(+) SMA, vimentin, CD68 in spindle cells
		Heavy admixed inflammatory infiltrate	(+) ALK-1
		Hyalinised collagenous stroma	(−) S-100, HMB-45, Mart1/MelanA, MiTF

*The ultrastructural hallmark of Langerhans cells is the rod-shaped or rocket-shaped granules (Birbeck granules, Langerhans cell granules), which may be needed to establish the diagnosis of Langerhans cell histiocytosis.
ALK-1, anaplastic lymphoma kinase-1; HMB, human melanoma black; MiTF, microphthalmia transcription factor; PGP, P glycoprotein; SMA, smooth muscle actin.