While the study cannot prove causation, the hypothesis offered by Dr Gardner and colleagues is a likely explanation, said Umang Swami, MD, assistant professor in the department of oncology at the Huntsman Cancer Institute at the University of Utah, Salt Lake City. “I believe the health interventions, the policy changes which we are trying to make are probably showing evidence in the real world,” he said.

In addition, federal data suggest a 10% decrease in the use of UV-emitting tanning beds among teenagers between 2009 and 2017, which could also help explain the decrease, Dr Swami added.3

Adewole Adamson, MD, MPP, assistant professor in the department of internal medicine at the University of Texas at Austin Dell Medical School, questions the assumption that increased sunscreen use would significantly lower melanoma rates. While epidemiological data suggest that UV exposure is associated with melanoma in non-Hispanic whites, it only increases risk slightly, and there is little evidence that sunscreen prevents melanoma, Dr Adamson argued.

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While there is strong evidence that sunscreen reduces the risk of developing other skin cancers such as squamous cell carcinoma, only 1 randomized clinical trial has so far examined the effect of long-term sunscreen use on melanoma development, and the results were barely statistically significant, he said.4

Studies have failed to find any association between UV exposure and melanoma incidence in black or Hispanic populations, he added.5 The fact that black individuals predominantly develop melanoma on parts of the body that are not typically exposed to sunlight — such as the palms of the hands and soles of the feet — also indicates that melanoma is not related to sun exposure among that subgroup, Dr Adamson explained. (Dr Adamson is on the American Academy of Dermatology Skin Cancer and Skin of Color Work Group and stressed that his views do not reflect those of the group.)

Dr Swami and Dr Adamson agreed that the new research can’t entirely rule out the possibility that changing racial demographics could play a role in driving the decrease in melanoma — US census data suggest that the population of non-Hispanic whites, who are most at risk for melanoma, is declining, and populations of color are expanding.6

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Dr Adamson also suggested that the decline in melanoma occurrence among younger cohorts could also reflect recent changes in how certain moles, known as Spitz nevus growths, are classified among adolescents. “Dermatopathologists have backed off from calling certain atypical moles ‘melanoma’ in adolescents because they don’t clinically behave like melanoma,” he wrote to Cancer Therapy Advisor in an email. “It’s possible that some of the decline [could be due to] a reclassification issue.”

Noteworthy in the discussion of the benefits of sunscreen are recent findings that ingredients contained in chemical sunscreens can leach into the blood. A randomized trial in 2019 run by scientists from the US Food and Drug Association found that following heavy sunscreen use, chemicals were detectable in human blood at levels that exceeded the agency’s toxicology thresholds.7 Although in the trial, sunscreen was used at levels far exceeding typical use, “more studies are warranted regarding the effects of these chemical sunscreens,” Dr Swami said.

To Dr Gardner, her study underscores the fact that there is still work to do in reducing melanoma incidence, particularly among older cohorts. “We’ve really been getting some incredible wins on the treatment of advanced melanoma, with immunotherapy and targeted therapy. But of course, it’s still easier to prevent than it is to cure, and were not done on either front.”  

Disclosure: Some of the authors of the Paulson et al study reported financial relationships with pharmaceutical or medical device companies, or related to patents. For a full list of disclosures, please refer to the original studies.

References

  1. Paulson KG, Dupta D, Kim TS, et al. Age-specific incidence of melanoma in the United States. JAMA Dermatol. 2020;156(1):57-64.
  2. Bray HN, Matthew CS, Zisansha et al. Head and neck melanoma incidence trends in the pediatric, adolescent, and young adult populations of the United States and Canada, 1995-2014. JAMA Otolaryngol Head Neck Surg. 2019;145(11)1064-1072.
  3. Centers for Disease Control and Prevention. Skin Cancer: Indoor tanning. Updated October 31, 2018. Accessed February 27, 2020.
  4. Green AC, Williams GM, Logan V, Strutton GM. Reduced melanoma after regular sunscreen use: randomized trial follow-up. J Clin Oncol. 2011;29(3):257-263.
  5. Eide MJ, Weinstock MA. Association of UV index, latitude, and melanoma incidence in nonwhite populations—US surveillance, epidemiology, and end results (SEER) program, 1992 to 2001. Arch Dermatol. 2005;141(4):477-481.
  6. Krogstad JM. Pew Research Center. Reflecting a demographic shift, 109 U.S. counties have become majority nonwhite since 2000. Published August 21, 2019. Accessed March 5, 2020.
  7. Matta MK, Zusterzeel R, Nageswara RP et al. Effect of sunscreen application under maximal use conditions on plasma concentrations of sunscreen ingredients. JAMA. 2019;321(21):2082-2091.

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Melanoma Skin Cancer