Season of initial discovery of tumour as an independent variable predicting survival in breast cancer.

The month of initial detection of tumour was recorded in 2,245 patients with breast cancer and correlated with survival over a follow-up period of 1.5-10 years. Women who initially detected their breast cancer in spring/summer had a significantly longer survival than those detecting their tumour at other times of the year. Overall, this relationship was independent of nodal status, tumour size and hormone receptor status. However, when patients were divided into groups the survival advantage was significantly associated with receptor status and age. Women aged greater than or equal to 50 years with ER-positive and PR-positive tumours who discovered their initial tumour in spring/summer had significantly better survival than those detecting their tumours at other times of the year. Survival was also longer in women aged less than 50 years with receptor-negative tumours who initially found their tumours in spring/summer compared with the rest of the year. This study suggests that the season of first detection of a breast cancer relates significantly to the later behaviour of the tumour, and may reflect seasonal changes in hormone dependent growth.