Season of tumour detection influences factors predicting survival of patients with breast cancer

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Abstract
The rate of initial detection of breast tumours varies during the year in a seasonal fashion, more tumours being discovered in late spring/early summer than at other times of the year. This phenomenon is particularly pronounced in young women (< 50 years) with progesterone receptor positive tumours. The present study investigates whether season of tumour detection influences the predictive capacity of several recognised prognostic and risk factors in patients with breast cancer. Axillary nodal status, tumour progesterone receptor status, and season of tumour detection significantly influenced survival in both older (> 50 yrs) and younger (< 50 yrs) patients. Parity, lactational history, body mass index, tumour oestrogen receptor status, and patient age also influenced survival, but these effects were significant only in age groups < 50 or > 50 yrs. Season of detection of tumour did not affect the prognostic significance of axillary nodal status. However, the effect of oestrogen receptor status on survival was more significant in patients who detected their tumours in the spring/summer compared with winter (odds ratio 0.52 and 0.73 respectively). Negative progesterone receptor status was associated with significantly poorer survival only in patients with tumours found in the winter. There was a significant survival disadvantage for nulliparous compared with parous women with breast cancer who were ≥ 50 years at diagnosis, and for women who had never lactated compared with those who had lactated, but this disadvantage was restricted to those who found their tumours in the summer. An increased body mass index (≥ 28) was associated with decreased survival, but this was significant only for those detecting tumours in winter. The increased incidence of detection of breast cancer in spring/summer may reflect cyclic influences on tumour growth. Such influences may be hormonal in nature and may underlie the effect of season of tumour detection on the prognostic influence of lactation, parity, body mass index, and oestrogen and progesterone receptor status in patients with breast cancer.