BOCA RATON, FLA. – Pediatric melanoma can be difficult to predict, as the known risk factors in adults typically don't apply in children, but one exception is in the setting of giant congenital melanocytic nevi.
Giant congenital melanocytic nevi (CMN) are rare, occurring in fewer than 1 in 100,000 live births, but the estimated incidence of soft tissue melanoma in association with such nevi, based on a number of retrospective studies, is about 4%, said Dr. Seth J. Orlow at the annual meeting of the Florida Society of Dermatology and Dermatologic Surgery.
Dr. Seth J. Orlow
Interestingly, the risk of melanoma of the central nervous system or other internal site is slightly higher at about 5% (J. Am. Acad. Dermatol. 1979;1:123-300) , said Dr. Orlow, chair of dermatology and a professor of pediatric dermatology at New York University.
The risk of melanoma in association with giant CMN across the lifetime is up to 10%. The risk appears based on findings from several prospective trials that half of that risk is concentrated in the first 5 years of life, he said.
The greatest risk, in his experience, is in children with giant CMN involving the scalp or posterior axial location, and in particular in those with satellite congenital nevi.
"The child who is born with multiple small congenital nevi – in fact, even if they don't have a giant congenital nevus with multiple small congenital nevi – has a risk factor," he said. Giant CMN by itself doesn't seem to be much of an issue, he noted.
To date there have been no reports of melanoma developing within a satellite nevus, despite some of these patients having up to 100 congenital nevi for years, he said.
When melanomas do arise in patients with giant CMN, they can be very difficult to recognize early, he added. In addition to those that arise in the central nervous system, some develop in the dermis or below, and in some cases no primary site can be found.
The risk of melanoma in children who have medium-sized CMN is much lower than with giant CMN and is estimated at less than 0.1% over the lifetime, he noted.
In one study of 227 patients with medium CMN followed for nearly 7 years, no melanomas developed (J. Am. Acad. Dermatol. 1998;39:428-33). Findings from another study involving information from the National Cancer Institute’s Surveillance, Epidemiology, and End Results (SEER) Program database showed that the risk is about 1 in 10,000 patients before puberty, and 1 in 4,000 patients over the lifetime (Pediatr. Dermatol. 1994;11:204-8).
Thus it appears that most of the medium CMN occur after puberty, and they tend to arise at the dermal-epidermal junction, Dr. Orlow said.
The risk with small CMN can't be quantified, but is "much, much, much lower," he said.
Dr. Orlow had no disclosures relevant to his presentation.