Incidence of cutaneous malignant melanoma in Iranian provinces and American states matched on ultraviolet radiation exposure: an ecologic study.

OBJECTIVES: Ultraviolet radiation (UVR), with UVB and UVA as the relevant components, is a risk factor for melanoma. Complete ascertainment and registration of melanoma in Iran was conducted in five provinces (Ardabil, Golestan, Mazandaran, Gilan and Kerman) during 1996-2000. The aim of our study was to compare population-based incidence data from these provinces with rates in the United States (US) while standardizing ambient UVR.

METHODS: Population-based rates representing all incident cases of melanoma (1996-2000) across the five Iranian provinces were compared to rates of melanoma among white non-Hispanics in the US. Overall age-standardized rates (ASR) for Iran and the US (per 100,000 person-years adjusted to 2000 world population) and standardized rate ratios (SRR) were calculated. We measured erythemally-weighted average solar UVR exposures (with contributions from both UVB and UVA range) of the five Iranian provinces using data from NASA's Total Ozone Mapping Spectrometer and selected five US states (Kentucky, Utah, Texas, Oklahoma, and Hawaii) with matching UVR exposure to each province. Incidence rates of melanoma during 1996-2000 in each Iranian province were compared to rates among white non-Hispanics in its UVR-matched US state.

RESULTS: The overall male and female ASRs of melanoma were 0.60 (95%CI: 0.56-0.64) and 0.46 (95%CI: 0.42-0.49), respectively, for Iran and 22.78 (95%CI: 22.42-23.14) and 16.61 (95%CI: 16.30-16.92) for the US. SRRs of melanoma comparing US to Iran were 37.97 (95%CI: 35.78-40.29) for males and 36.11 (95%CI: 33.69-38.70) for females, indicating significantly higher incidence in the US. ASRs and age-specific rates of melanoma for both genders were significantly lower in each Iranian province compared to its UVR-matched US state.

CONCLUSION: The markedly lower incidence rates of melanoma in Iranian provinces with similar UVR exposures to US states underscore the need for additional comparative studies to decipher the influence of other extrinsic and intrinsic factors on the risk of this malignancy.