Features of Spitzoid lesions
| Feature | Spitz naevus | Atypical Spitz tumour | Spitzoid melanoma |
| Clinical | |||
| Age | Any age (2/3 < 20 years) | No difference | No difference |
| Location | Any location (extremities and trunk preferred; H&N in children) | No difference | No difference |
| Colour | Red–brown; occasionally pigmented | No difference | No difference |
| Silhouette | |||
| a. Size | Small (most <6 mm) | Variable | Large (>10 mm) |
| b. Symmetry | Present | Variable | Asymmetrical |
| c. Circumscription | Present | Variable | Poor |
| Evolution/clinical course | Stable | May metastasise to regional LNs; natural history uncertain | Variable malignant course: regional LN mets but favourable outcome to widely metastatic disease and death |
| Architectural | |||
| Epidermis | |||
| Silhouette | |||
| a. Size | Small | Variable | Large |
| b. Symmetry | Present (must evaluate fully excised lesion) | Variable | Asymmetrical |
| c. Circumscription | Present (must evaluate fully excised lesion) | Variable | Poor |
| Epidermal hyperplasia | Present | No difference | May be atrophic/ulcerated |
| Artifactual clefting | Present | No difference | Variable |
| Kamino bodies | May be present (∼50% of cases—multiple levels increase detection) | No difference | No difference |
| Pagetoid spread | Often present | Variable | Prominent; present at edge of lesion or upper half of epidermis |
| Dermis/subcutis | |||
| Cellular density | Variable (low–moderate) | Moderate– dense | Dense (confluent growth) |
| Pattern of growth | Organised, nested and interstitial growth | Variable | Confluent, destructive |
| Architectural maturation | Present | Variable | Absent |
| Deep front of lesion | Infiltrative with outlier cells | Variable | Expansile or infiltrative |
| Involvement of subcutis | Rare—may be minimal | Variable | May be pronounced |
| Stromal/inflammatory response | Variable (usually mild) | Variable | Inflammation or regression may be noted |
| Cytological | |||
| Nuclear size | Moderate–large | No difference | Large |
| Nuclear shape | Normal–angulated | No difference | Pleomorphic |
| Cytoplasm | Abundant, eosinophilic ‘ground-glass’ | No difference | Variable |
| N/C ratio | Low | No difference | Variable |
| Multinucleation | Present | No difference | No difference |
| Hyperchromasia | Low–moderate | Variable | High |
| Nucleoli | Present (small–moderate sized) | Variable | Present (large) |
| Nuclear membrane | Normal | Variable | Irregular |
| Chromatin pattern | Dispersed | Variable | Coarse |
| Cytological maturation | Present | Variable | Absent |
| Other | |||
| Mitotic activity | Absent–moderate (up to 6 per 10hpf); confined to junction or superficial dermis | Variable | High (often >6 per 10hpf); abnormal or deep forms |
| Perineural or angiolymphatic invasion | Absent | Absent | May be present |
| Sentinel lymph node | Negative | May be positive | May be positive |
| Necrosis | Absent | Absent | May be present |
| Immunohistochemistry | |||
| HMB-45 | Variable (typically stratified) | Variable | Variable (often diffuse) |
| MIB-1 | Low proliferative index (<10%) | Variable (<15%) | High (>15%) |
| Cytogenetics | Normal or isolated gain of 11p | Intermediate–often complex aberrations | Complex chromosomal aberrations |
H&N, head and neck; LN, lymph node.