Conventional Spitz tumors | Atypical Spitz tumors | Melanoma | |
Architecture | |||
Diameter | <5 to 6 mm | ≥5 to 6 mm | ≥10 mm |
Outline | Symmetric (wedge shaped) | Asymmetric | Asymmetric |
Circumscription | Sharp, lateral circumscription | Often poor circumscription | Poor circumscription |
Epidermal hyperplasia | Present | Effacement of the epidermis may be present | Absent, or effacement of the epidermis may be present |
Maturation with dermal depth | Present | Possibly diminished or lack of zonation and maturation | Lack of zonation and maturation often present |
Eosinophilic hyaline globules (Kamino bodies) | Present | Absent or few | Typically absent |
Cellular density | Orderly, nondisruptive infiltration of collagen by melanocytes | High cellular density | High cellular density |
Cytology | |||
Cellular population | Uniform spindle and/or epithelioid | Spindle and/or epithelioid cells showing increasing cytologic atypia | Spindle and/or epithelioid cells showing increasing cytologic atypia and pleomorphism |
Cytoplasm | Opaque or ground glass cytoplasm | Granular versus ground glass cytoplasm | Granular or mixed cytoplasm |
Nuclear-to-cytoplasmic ratio | Low nuclear-to-cytoplasmic ratio | Increasingly high nuclear-to-cytoplasmic ratio | High nuclear-to-cytoplasmic ratio |
Chromatin pattern | Nuclei with open, delicate chromatin pattern | Loss of delicate or dispersed chromatin pattern | Loss of delicate or dispersed chromatin pattern |
Nucleoli | Uniform nucleoli | Increasingly prominent nucleoli | Large nucleoli |
Pleomorphism | Rare | May be present | Usually present |
Hyperchromatism | Absent | May be present | Present |
Proliferation | |||
Mitotic rate | <2/mm2 Absent or rare mitoses in deep dermis Lack of atypical mitoses | 2 to 6/mm2 (particularly >6/mm2) Deep or marginal dermal mitoses may be present | 2 to 6/mm2 (particularly >6/mm2) Deep or marginal dermal mitoses frequently present |
Proliferative index (Ki-67 expression) | <2% | 2 to >10% | Often >15 to 30% |
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