Finally, Evidence That Sunscreen Delivers

Primary melanomas developed less often with daily, rather than discretionary, sunscreen use.
Routine sunscreen for melanoma prevention is a recommendation almost written in stone. Sunburns are associated with melanoma risk, and sunscreens were designed to minimize sunburns, but logic, not evidence, dictated that sunscreen use would reduce melanoma risk. Now, direct clinical evidence may finally be available.
Between 1992 and 1996, 1621 randomly selected Australian residents aged 25 to 75 were randomized to daily or discretionary sunscreen use, plus supplementation with 30 mg beta carotene or placebo, and observed for incidence of primary melanoma. The subjects in the sunscreen group received an unlimited supply of SPF16 sunscreen and instructions to apply it to head, neck, arms, and hands. Compliance was determined by questionnaire results and by weighing returned sunscreen bottles. Although no sunscreen was supplied after 1996, participants continued to answer questions about sun exposure, sunscreen use, and melanoma formation until 2006. New melanoma diagnoses were confirmed through pathology reports and the Queensland Cancer Registry.
By the study’s end, 846 people (52%) were actively completing questionnaires, 600 (37%) were passive participants, and 173 (11%) had died. No between-group differences were observed during or after the trial in sun exposure or sun protection other than sunscreen use. Eleven people in the daily-sunscreen group and 22 in the discretionary-use group developed a primary melanoma by the end of follow-up.
Risk for developing any melanoma was reduced by 50% and risk for invasive melanoma was reduced by 73% in daily users compared with discretionary users (P=0.051 and P=0.045, respectively). There were no significant between-group differences in either in situ melanomas or melanomas at prescribed application sites. No direct effects of beta carotene were discernible.
Comment: This large, community-based sunscreen trial is likely the last of its scope. The findings won’t change sunscreen recommendations but do provide clear support for its use. Sunscreen alone is insufficient to eliminate melanoma risk, and the effects of all-form sun protection on melanoma mortality are unknown. Also, these findings leave unaddressed sunscreen use in less-sunny locations and in populations with other skin tones. Nevertheless, this carefully executed and ambitious study is commendable. The same trial has already shown reduced squamous cell carcinoma risk, so its clinical implications are compelling. One could question the borderline significance of the risk reductions, or note that the incidence of melanoma versus non-melanoma skin cancers undermined the study’s power from the beginning, but the author of an accompanying editorial carefully outlines the statistical rigor of this trial.
— Hensin Tsao, MD, PhD