Seasonality in the Incidence of Breast Cancer in Teenage and Young Adult Females in Northern England, 1968-2005

There are few studies that focus on risk factors for breast cancer in teenagers and young adults. Known risk factors for breast cancer in females include family history of breast cancer and environmental exposure to carcinogens. Seasonal variation suggests that environmental factors may be involved in aetiology. The aim of this study was to investigate seasonal variation in breast cancer incidence among 15-24 year old females. Details of 42 cases, diagnosed during 1968-2005, were extracted from a specialist registry. Seasonal variation was analysed with respect to months of birth and diagnosis using the chi-squared heterogeneity test to examine non-uniform variation. Poisson regression analysis was used to fit sinusoidal models. There was significant heterogeneity for breast carcinoma (P = 0.045), based on month of birth showing evidence of a seasonal effect. This finding of seasonal variation around time of birth amongst females with breast carcinoma is highly novel and suggests a possible early aetiological involvement of environmental factors.