Table 1 Benign non-melanocytic mimics of intradermal melanoma
LesionClinical featuresHistologyImmunohistochemistry
ScarPrevious trauma or iatrogenic proceduresScattered spindle cellsOccasionally focally S-100 (+) fibroblasts (cytoplasmic pattern)
Mild cytological atypia(+) SMA focally
Might be mitotically active (depending on the age of the scar)(−) HMB-45
(−) Mart1/Melan A
(−) MiTF
Inflammatory pseudotumourSolitary papules and nodulesMature plasma cells, lymphocytes(+) SMA, vimentin, CD68, PGM-1 in spindle cells
Bland-looking spindle cells arranged in fascicular pattern(+) ALK-1 in IMT
(−) S-100, HMB-45, Mart1/MelanA, MiTF
Epithelioid cutaneous fibrous histiocytomaMiddle-aged adultsPredominant epithelioid cells, separated by hyalinised collagen (keloidal type)(+) FXIIIa
No gender preferenceMultinucleated giant cells(+) Diffuse CD10
(+) Focal S-100 dendritic cells
(±) Stromelysin-II
(+) CD68 (granular pattern)
(−) CD34
(−) S-100
(−) HMB-45
(−) Mart1/Melan A
(−) MiTF
Cellular cutaneous fibrous histiocytomaYoung or middle-aged adultsEosinophilic spindle cells in fascicular pattern(+) Factor XIIIa
Male predominanceModerate mitotic rate(+) HMGA1, HMGA2
Head and neck, extremities(+) Diffuse CD10
(+) CD68 (granular pattern)
(±) Stromelysin-II
(−) S-100
(−) HMB-45,
(−) Mart1/Melan A
(−) MiTF
Xanthogranuloma (adult and juvenile types)Head and neckMultinucleated giant cells(+) Vimentin
Touton giant cells(+) CD 68
Spindle cells(+) α-1 Antitrypsin, α-1 antichymotrypsin
Chronic inflammatory cells.(+) CD10
(+) Factor XIIIa
(−) S-100 (dendritic cells can be focally positive)
(−) CD1a
(−) HMB-45
(−) Mart1/Melan A
(−) MiTF
Cellular neurothekeomaFemale predominance in twentiesEpithelioid and spindled cells arranged in fascicules and nodular aggregates(+) NKI-C3 (non-specific)
Head and neck, upper extremitiesPleomorphism(+) Leu-7 (CD57)
Low mitotic rate(+) NSE
(+) MiTF
(+) MMP-II
(+) PGP 9.5
(+) CD10
(+) CD68
(+) Vimentin
(+) SMA
(+) Focal factor XIIIa
(−) S-100
(−) HMB-45
(−) Mart1/MelanA
Reticulohistiocytoma (solitary epithelioid histiocytoma)Young adultsHistiocytes with ground-glass cytoplasm(+) CD163
Male predominanceLymphocytes and neutrophils(+) CD68
Mild mitotic activity(+) Variably α-1 antitrypsin
(+) Lysozyme
(+) Vimentin
(+) MSA
(+) Focal factor XIIIa
(+) Focal S-100
(−) HMB-45
(−) Mart 1/Melan A
(−) MiTF
Granular cell tumourSolitary painless nodulePlump, spindle and epithelioid cells with abundant eosinophilic cytoplasm and inconspicuous bland nuclei(+) S-100
Twice as common in women as in menCells mainly in the superficial dermis with varying degree of epidermal extension(+) Calretinin
(+) Inhibin
(+) CD68
(−) Mart 1/Melan A
(−) HMB-45
(−) MiTF
PEComaDepends on type and site of PEComaClear or eosinophilic spindle-epithelioid cells(+) HMB-45
Fascicular, nested, sheet-like patterns(+) Mart1/MelanA
Perivascular accentuation(+) MiTF
Multinucleated giant cells(+) S-100 in 33%
Size <8 cm, mitotic count <1/50 HPFs, no necrosis(+) SMA, MSA
(+) Desmin
(+) Cyclin D1
(+) Vimentin
(+) Pan-cytokeratin
  • ALK-1, anaplastic lymphoma kinase-1; HMB, human melanoma black; HPF, high-power field; MiTF, microphthalmia transcription factor; MMP, matrix metalloproteinase; HHV, human herpesvirus; HMGA, high mobility group A; MSA, muscle specific actin; PGP, P glycoprotein; NSE, neuron-specific enolase; PEComa, perivascular epithelioid cell tumour; SMA, smooth muscle actin.