Chicago ? At age 10, freckle-faced Corey Halpin had bigger things to think about like basketball and Boy Scouts than the little black mole he noticed on his arm while camping.

At first, he thought it might be a tick. “I pushed it but it didn’t move, but it bled,” he recalled.

It wasn’t until a few months later, during a spring 2002 visit to his pediatrician, that Corey casually asked his dad if he should mention the odd mole. That led to a referral to a specialist and alarming test results that caught even his doctors by surprise.

Melanoma, the most serious and potentially deadly form of skin cancer, was until recently almost unheard of in children, and it was a diagnosis that his family wasn’t prepared for.

“My husband and I were scared to death” and so was Corey, said his mother, Marge Halpin.

Pediatric melanoma is still uncommon in children, affecting only 7 per million, or about 500, according to 2002 statistics from the National Cancer Institute. But that number has risen from 3 per million in 1982.

Dr. Charles Balch of the American Society of Clinical Oncology, who has specialized in melanoma for 30 years, saw his first pediatric case five years ago. Since then, Johns Hopkins Hospital, where he works, has treated about 20 youngsters, the youngest just 8 years old.

Dr. Anthony Mancini, dermatology chief at Children’s Memorial Hospital in Chicago, diagnosed Corey Halpin’s melanoma and said he and his colleagues have treated eight cases in the past nine years, about double the number seen in the previous two decades.

Corey Halpin, 13, shows off his scar, a reminder of surgery three years ago to remove a cancerous growth. Doctors discovered melanoma on Corey's left arm when he was just 10. The most serious and potentially deadly form of skin cancer was almost unheard of in children until recently.

Recent studies also report increases in England, Sweden and Australia.

“There’s an appropriate level of alarm here,” Mancini said. “Clearly it’s happening and it’s deadly, and it’s missed.”

Some pediatricians who see unusual moles in children “would ordinarily dismiss this as nothing because melanoma is not supposed to happen in this age group,” Balch said. “We all should be aware that this can occur and biopsy suspicious or changing moles in children.”

Balch said reasons for the increase are uncertain. Some doctors think it might be from depletion of the ozone layer, which protects the Earth from some of the sun’s damaging ultraviolet radiation. Others attribute it to excessive sun exposure and blistering sunburns in early childhood.

Melanoma prevalence has risen in adults, too — more than doubling in the past 30 years, according to the cancer institute. The American Cancer Society estimates that this year about 60,000 U.S. adults will be diagnosed with melanoma and that 7,700 will die from it.