Southern California has the third highest rate of melanoma in the world, only behind Australia and New Zealand. These statistics fly in the face of long-held conventional wisdom that skin cancer preys only on people with fair complexions. More than half of Southlanders are Latino, and nearly 10 percent are African-American.
While it’s true that nonmelanoma skin cancers strike mostly Caucasians, melanoma — the least common but most deadly form of skin cancer — is a concern for all racial and ethnic groups.
“The melanoma rate among Hispanics is certainly lower than in whites,” explained USC epidemiologist Myles Cockburn, “but it’s increasing rapidly, and it’s the worst kind of melanomas that are becoming more common in Hispanics. Twenty or 30 percent of all late-stage melanomas we see in LA County are now in Hispanics.”
African-Americans, meanwhile, have the highest rate of the rare but deadly melanomas found on the feet — extremities that normally get little sun exposure.
Cockburn’s group at the Keck School of Medicine of USC was the first to publish data showing an alarming increase in melanoma risk among nonfair-skinned, nonwhite people.
“We recommended to the National Institutes of Health that they never again fund a melanoma study that only looks at white people — which is basically all research done to date,” Cockburn said. Evidence notwithstanding, it remains an uphill battle to persuade dermatologists to administer skin exams to dark-skinned people, so pervasive is the mistaken belief that they aren’t at risk. Dermatology residents at the Keck School, through Cockburn’s efforts, labor under no such illusions.
He is spreading the word beyond the medical profession. A recent four-year, $3.2 million National Institutes of Health grant is aimed at alerting youngsters in the heavily nonwhite Los Angeles Unified School District to their risk.
No one knows why melanoma is so prevalent in Southern California, New Zealand and Australia. In future research, Cockburn’s group will look specifically at his native New Zealand. Given its location near Antarctica, far from the sun-soaked Equator, the southwestern Pacific nation’s high melanoma rate seems perplexing.
But the relationship between sunburn and melanoma isn’t very strong, Cockburn said. “We think that’s because the type of sun exposure that causes sunburn is different from the type that causes melanoma.”
Focusing narrowly on ultraviolet A and ultraviolet B rays is a mistake, he believes. While closely associated with sunburn and sun-related skin damage, these specific wavelengths are merely two arbitrary ranges in a broad spectrum of possible kinds of light — from visible to invisible ultraviolet.
“All wavelengths have different energies when they hit your skin. One range has an immediate effect on your skin’s inflammatory response,” he said. “Others may be nestling their way between the cells in your skin, breaking up your DNA in a way that can’t be repaired.”
Cockburn thinks further research will show a strong behavioral component in melanoma incidence. After all, different kinds of light will prompt different social behaviors. A very short wavelength — the kind produced by the midday sun — results in sunburn almost immediately, prompting reasonable people to cover up or seek shelter quickly. A longer wavelength — the kind emitted at 4 p.m. — won’t cause sunburn or produce intense heat, emboldening people to stay out longer and forgo sunscreen, hats or long sleeves. All the while, the damaging ultraviolet light is penetrating their skin, triggering mutations that may lead to melanoma years later.
“That might explain some of the complexity of sun exposure in melanoma,” Cockburn said. It might also explain why the deadliest melanomas tend to strike dark-skinned people — those who are less prone to sunburn and have been lulled into the false belief that they are not at risk for skin cancers.