Objective: Because most risk factors for melanoma are immutable constitutional factors such as skin type, it is important to more fully understand the relationship between melanoma risk and sun exposure, one of the few modifiable risk factors for the disease. The goal of this case-control study was to quantify the risks of melanoma associated with UV exposure at different periods of life.
Methods: Cases were 386 patients between the ages of 35 and 74 who were diagnosed with primary cutaneous melanoma within the Seattle-Puget Sound area during 1997. Controls were 727 participants of the same age and geographic area, selected by random-digit dialing. A telephone interview included a complete residential history, lifetime sun exposure history (days in the summer sun for at least 4 h at each place of residence), and personal characteristics. UV exposure was calculated based on satellite data on potential erythemal exposure at each place of residence, years at each location and time spent in the sun at each location. Logistic regression was used to estimate odds ratios (OR) and 95% confidence intervals (CI) reflecting the risk of melanoma associated with UV exposure, after adjustment for age, sex, income, tendency to burn and sunburns during ages 2-10.
Results: Among women, lifetime UV exposure was associated with melanoma risk (adjusted OR = 1.99 for highest versus lowest quartile, 95% CI: 0.95-3.03, p for trend = 0.008). There were significant trends for UV exposure during ages 1-10, 11-20 and 31-40 (all p < 0.02). Among men, there were no significant associations at any time period, but lifetime UV exposure was associated with higher risk for men who had a tendency toward severe or painful sunburns (OR = 2.85 for highest versus lowest quartile, 95% CI: 0.84-9.64, p for trend = 0.04).
Conclusion: The differing results by sex are not easily interpretable, though it may be useful to target those with a higher sensitivity to the sun when formulating messages for prevention of melanoma by lowering exposure to UV.