Seasonal variations in breast cancer diagnosis in Osaka, Japan

To date, seasonal variations in breast cancer diagnosis have been reported in Western countries. In the present study, we calculated the number of breast cancer diagnoses according to season between 1976 and 2005, using data from the Osaka Cancer Registry. In all time periods and all age groups, breast cancer diagnosis showed peaks in early summer and troughs in winter. The number of breast cancer diagnoses in the spring, summer, autumn, and winter were 2,595(26%), 2,739(27%), 2,585(26%), and 2,120(21%)in 1976-1985; 4,219(26%), 4,581(28%), 4,2 62(26%), and 3,466(21%)in 1986-1995; and 6,299(25%), 6,852(28%), 6,368(26%), and 5,335(22%)in 1996-2005, respectively. Most cases were diagnosed because of an awareness of a breast mass. The trend in screening-detected cases differed from the overall trend. As screening becomes more widely adopted, these seasonal variations might change. Careful monitoring is needed to confirm these findings.