Impact of seasonal and geographical differences on breast cancer survival

Abstract

Purpose: Seasonal and geographic variations in ultraviolet B intensities (UVB) impact the vitamin D status, and these differences might significantly affect cancer prognosis. This study evaluates the association between seasonal and geographic differences in UVB exposure and breast cancer survival. Methods: We divided Korea into two regions according to erythemally weighted annual UVB exposure as follows: Seoul and the southern region. Recurrence and death were also grouped into two seasons: spring/summer and autumn/winter. Results: The survival and relapse rates, when stratified by season of diagnosis, demonstrated no significant differences between spring/summer and autumn/winter. Among the 1,488 breast cancer patients in our cohort who demonstrated recurrence, 775 cases (52.1%) relapsed during the spring/summer and 594 patients (52.6%) died during the autumn/winter. In total, 6,178 patients (89.1%) and 3,909 patients (91.3%) in Seoul and the southern region survived (P=0.005). The relapse rate in the Seoul group (13.7%) was higher than the southern group (11.9%). By Kaplan-Meier analysis, there were no statistical differences between the Seoul and southern groups in terms of disease-free (P=0.43) and cancer-specific survival (P=0.18). In the Cox analysis, after the adjustment of all the other factors, season of diagnosis and residential area have no statistical significance. Conclusion: We conclude from our findings that death from breast cancer occurs more frequently in the autumn/winter, and that patients in the southern area of Korea demonstrate better survival. However, we find no significant relationship between geographic and seasonal variations in breast cancer survival.