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.