Histologic features of atypical Spitz tumors

Architecture

• Diameter usually >5 and often >10 mm

• Involvement of the subcutaneous tissue

• Ulceration

• Poor circumscription

• Extensive pagetoid scatter

• Effacement of the epidermis

• Prominent confluence of melanocytes

• High cellular density

• Lack of zonation and maturation

• Asymmetry

• Absent or few eosinophilic hyaline globules (Kamino bodies)

Proliferation

• Significant mitotic rate (2 to 6/mm²) (particularly >6/mm²)

• Deep or marginal dermal mitoses

• Proliferative index (Ki-67 expression)

- Between 2 to 10 percent^[1]

- ≥10 to 15 percent^[2]

Cytology

• Granular versus ground glass cytoplasm

• High nuclear to cytoplasmic ratio

• Loss of delicate or dispersed chromatin pattern

• Thickening of nuclear membranes

• Hyperchromatism

• Large nucleoli

References:

Vollmer RT. Use of Bayes rule and MIB-1 proliferation index to discriminate Spitz nevus from malignant melanoma. Am J Clin Pathol 2004; 122:499.
Kapur P, Selim MA, Roy LC, et al. Spitz nevi and atypical Spitz nevi/tumors: a histologic and immunohistochemical analysis. Mod Pathol 2005; 18:197.

Reprinted by permission from Macmillan Publishers Ltd: Modern Pathology. Barnhill RL. The Spitzoid lesion: Rethinking spitz tumors, atypical variants, 'Spitzoid melanoma' and risk assessment. Mod Pathol 2006; 19 Suppl 2:S21. Copyright © 2006.

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Histologic features of atypical Spitz tumors