Spindle and Epithelioid Cell Nevus (Spitz Nevus)

(Benign Juvenile Melanoma)

Epidemiology:

• Children and young adults

Common sites:

• Head and neck (face)
• Upper extremities

Gross features:

• Small (<1cm)
• Solitary
• Dome-shaped dermal nodule
• Prominent vasculature
• Relative lack of melanin pigmentation usually
• Red-pink or flesh-coloured
• May be multiple
• Grouped
• disseminated

Histologic features:

• May be junctional, compound, or dermal
• Usually prominent dermal component
• Symmetric architecture
• Abrupt attenuation of junctional nests at the lateral borders
• Broad base superficially, tapering to a narrow point in the deep dermis (imperfect triangle)
• Lack of deep extension
• Propensity for adnexal involvement
• Discohesive and infiltrative overall pattern
• Occasional pagetoid epidermal spread of epithelioid melanocytes
• Not prominent
• Maturation is present
• smaller cells at deep aspect
• Varying proportions of spindle and epithelioid melanocytes
• Spindle cells in fascicles arrayed perpendicular to the epidermis
• Elongated
• Fusiform
• Plump often
• Dendrites sometimes
• Abundant amphophilic cytoplasm
1. ground glass appearance
• Epithelioid cells dispersed individually throughout the lesion
• Large
• Round to oval, polygonal, rhomboidal, polyangular
• Distinct cellular borders
• Abundant amphophilic cytoplasm
1. ground glass appearance
• Extreme pleomorphism may be present in some cells, particularly in epithelioid cells
• Large nucleus with irregular contours (same size or larger than keratinocytes)
1. sometimes lobulated
• Prominent eosinophilic nucleolus
• Open or vesicular
• Lacking coarse, anaplastic features typical of malignant cells
1. fine / vesiculated chromatin
• Nuclear pseudoinclusions
• Multinucleated cells often
• Overwhelming majority of cells have a benign cytologic appearance
• Overall uniformity of cells and nuclei
• Mitoses may be present
• No deep mitoses (except rarely)
• No atypical mitoses (excelpt rarely)
• Eosinophilic hyaline-like globules near dermal-epidermal junction (Kamino bodies)
• Found less frequently in melanoma, but nonspecific
• PAS-positive (basement membrane components
• Artifactual separation of papillary dermal nests from overlying epidermis
• Vascular and edematous stroma
• Lymphocytic infiltration not uncommon
• Tends to be perivascular but may be diffuse
• Epidermal hyperplasia is common
• Densely sclerotic stroma in some
• Atypical Spitz nevus:
• Controversial
• Differentiation from melanoma is blurred
• Risk factors for metastasis:
• Age > 10y
1. the older the bigger the risk, esp >30y
• Size > 1cm
• Involvement of subcutaneous fat
• Ulceration present
• Mitotic activity per mm-squared (>5 is moderate, >9 is higher risk)
• Other factors to consider
• Family history of melanoma
• Location of lesion
1. back is uncommon for Spitz
• Clinical appearance
• History of recent change in a longstanding stable lesion
• Atypical Intraepidermal component:
• Asymmetry
• Irregular pattern in the epidermis
1. lentiginous proliferation
2. significant variation in size, shape, orientation, spacing of junctional nests
3. horizontal confluence/bridging of nests
• decreased cellular cohesion
• cytologic atypia beyond normal for Spitz
• Intraepidermal Spitz Nevi with prominent pagetoid spread (pagetoid Spitz):
• Lower extremities of young women commonly
• Most less than 5-6mm
• Overall symmetry maintained
• Sharp circumscription overall maintained
• Devoid of melanin usually
• Both single cells and nested
• Clefting usually present
• Pagetoid spread is usually limited, but may be prominent
• Atypical dermal component:
• Cohesive cellular nodules
• Increased cellularity
• Asymmetry
• Deep extension into deep dermis or subcutaneous fat
• Lack of maturation
• Orderly infiltration of collagen
• Cytologic atypia above normal for Spitz
1. should be relatively focal
• Deep mitotic activity
• Metastasizing Spitz nevus:
• See risk factors above
• Should be treated as melanoma

Immunophenotype:

Marker:

Sensitivity:

Specificity:

Molecular features:

•  HRAS mutations (10-20%)
• 11p gain (20%)
• Not found in melanoma

Other features:

• may rarely be a precursor of melanoma
• “malignant Spitz nevus” may metastasize to nodes (rare)

References:

• Sternberg 2004
• Barnhill 2004