Affiliations of authors: Section of Medical Statistics, University of Oslo, Oslo, Norway (MBV); Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden (EW, HOA); International Agency for Research on Cancer, Lyon, France (EW); Institute of Community Medicine, University of Tromsø, Tromsø, Norway (EL); School of Public Health, University of Sydney, Sydney, Australia (BA); Department of Epidemiology, Harvard University, Boston, MA (HOA).
Correspondence to: Marit B. Veierød, PhD, Section of Medical Statistics, University of Oslo, P.O. Box 1122 Blindern, N-0317 Oslo, Norway (e-mail: marit.veierod{at}basalmed.uio.no).
We thank Boniol et al. for their insightful comments and suggestions for future analyses. The hypothesis they propose is similar to hypotheses we plan to address in the future. However, we will require a larger number of incident cases of malignant melanoma for further analyses of subgroups and interactions between risk factors to have meaningful statistical power. We expect to obtain the additional cases after an additional 35 years of follow-up.
We are also grateful for the constructive comments and suggestions from Lazovich et al. In Norway and Sweden (as in the United States), tanning devices that used fluorescent tube lamps with high levels of UVA relative to the levels of UVB were introduced in the late 1970s, and commercial tanning salons became common around 1980 (Saxebøl G, Wester U: personal communications). However, the sale of medium-pressure mercury lamps (i.e., lamps with high levels of UVB relative to UVA) for tanning purposes was banned in 1983 in Norway and Sweden (Saxebøl G, Wester U: personal communications). Thus, as suggested by Lazovich et al., we evaluated whether women who used solaria before 1983 had a higher risk of melanoma than women who used solaria after 1983, after adjusting for age and other variables.
To determine solarium use before and after 1983, we considered how solarium exposure was recorded in the Norwegian-Swedish Women's Lifestyle and Health Cohort Study. Women born between 1943 and 1962 were recruited to our study in 1991 and 1992 and asked to report their frequencies of solarium use when they were 1019, 2029, 3039, and 4049 years old (1). We thus focused our analysis on the women who reported solarium use (1 time/month) when they were 2029 years of age, because solarium use was rare among women when they were 1019 years old (1) and because only 12% of the women were 3039 years old in or before 1983 and very few of them reported solarium exposure one or more times per month. We previously reported that the estimated relative risk (RR) of cutaneous malignant melanoma associated with the use of a solarium one or more times per month relative to no use at age 2029 was 2.58 (95% confidence interval [CI] = 1.48 to 4.50) (1).
Women who were 29 years old before or during 1983 were 2029 years old from 1963 through 1983 (i.e., before a ban on the sale of tanning lamps with high levels of UVB relative to UVA), whereas women who were 29 years old after 1983 were 2029 years old from 1975 through 1991. Thus, none of the women in the cohort lived the whole 2029 age decade after 1983. After close inspection of the relationship between age and calendar year, we constructed a variable for calendar year of exposure comprising three categories: women aged 29 before or during 1983 (i.e., women exposed from 1963 through 1983), women aged 29 after 1983 and aged 25 before or during 1983 (i.e., women exposed from 1975 through 1987), and women aged 25 after 1983 (i.e., women exposed from 1979 through 1991). Lazovich et al. reported that only 10% of individuals who had tanned indoors were doing so prior to 1980. Among women in our study who used a solarium one or more times per month at age 2029, only 18% had all of their exposure before or in 1983.
We also constructed a new exposure variable by combining solarium use at age 2029 and the variable for calendar year of exposure (Table 1). For solarium use, we included only the categories Never and 1 time/month (i.e., women who reported that they rarely used a solarium were excluded). We found that women who used a solarium one or more times per month at ages 2029 years before 1983 had a statistically significantly higher risk of melanoma than women who had never used a solarium at ages 2029 years (RR = 3.75, 95% CI =1.73 to 8.13). However, we also found that women who used a solarium one or more times per month at ages 2029 years mainly after 1983 (i.e., from 1979 through 1991) had a statistically significantly higher risk of melanoma than women who had never used a solarium at ages 2029 (RR = 3.19, 95% CI = 1.22 to 8.32) (Table 1). However, because there were so few cases in each of these categories, firm conclusions cannot be made until we have a larger number of incident cases.
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REFERENCE
1 Veierod MB, Weiderpass E, Thorn M, Hansson J, Lund E, Armstrong B, et al. A prospective study of pigmentation, sun exposure, and risk of cutaneous malignant melanoma in women. J Natl Cancer Inst 2003;95:15308.
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