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Childhood melanoma pathology

Author: A/Prof Patrick Emanuel, Dermatopathologist, Auckland, New Zealand, 2014.

Melanoma in childhood is fortunately rare but often presents at a late clinical stage due delays in biopsy and diagnosis. Predisposing factors are thought to be similar to adult melanoma.

Histology of childhood melanoma

Childhood melanoma may occur within a giant congenital naevus or can present as Spitzoid, nodular or superficially spreading types of melanoma.

The case illustrated here shows a nodular melanoma arising on the arm of a 8 year old boy (figures 1-5). This tumour shows: ulceration, lack of dermal maturation, dermal mitoses, pagetoid invasion of the epidermis and nuclear pleomorphism.

Special studies of childhood melanoma

Given the reluctance of making this diagnosis in children, ancillary studies such as FISH and CGH can be helpful in increasing diagnostic confidence. FISH was performed on the case illustrated herein and showed numerous abnormalities, as would be expected for melanoma.

Immunohistochemical studies may be helpful to illustrate high proliferative rates (Ki-67), and pagetoid invasion (Melan-A).

Abnormal FISH shows RREB1 (6p25; red probe) Gain; MYB (6q23, yellow) Loss

Differential diagnosis of childhood melanoma

Spitz naevus – Difficult cases may need external consultation and cytogenetic analysis.

Proliferative nodules within congenital naevi – Difficult cases may need external consultation and cytogenetic analysis.

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