Pediatric Melanoma

Pediatric melanoma is a rare entity, accounting for less than 1% of all melanoma cases. Most pediatric melanomas develop sporadically (de novo) without a known underlying condition or genetic predisposition. For example, alterations in the melanoma susceptibility gene CDKN2A, which are found in 25% to 50% of familial melanomas, are present in only less than 2% of pediatric patients at the germline level.

Substantial evidence suggests that the biologic behavior of melanocytic tumors in the pediatric population is distinct from that of histologically similar lesions in older patients. Even within the pediatric age group, the natural history and most common histologic subtypes seen in prepubescent patients are significantly different from those seen in postpubescent patients. For these reasons, it is diagnostically useful to consider the differences between pediatric and adult melanomas, as well as between childhood (prepubescent) and adolescent (postpubescent) melanomas.

There are three major subtypes of pediatric melanoma: the adult subtype, the spitzoid subtype, and the congenital nevi–associated subtype. Most childhood melanomas (those occurring in patients arbitrarily aged ≤10 years) are spitzoid melanomas, which is a subtype considered as low-grade/borderline on the spectrum of malignancy and which often have an excellent prognosis. However, an infrequently observed subtype of childhood melanomas that is associated with the presence of large/giant congenital nevi tends to be aggressive and often rapidly fatal. This subtype, although uncommon, is disproportionately observed in childhood patients as compared with adolescents or adults.

Of adolescent melanomas (those occurring in patients arbitrarily aged 11 to 18 years), approximately half are the spitzoid subtype. However, adolescent spitzoid melanomas have a more diverse clinical spectrum and a less predictable prognosis than those occurring in childhood. The remaining adolescent melanomas are the adult-subtype melanoma (also referred to as the “pediatric adult” subtype or the “conventional” subtype), so named because this subtype shares many morphologic and molecular features and a similar course of disease as adult melanoma. It is unknown why prepubescent children are less prone to the adult subtype of melanoma than are adolescents.