Stress and breast cancer

Editor—One of the main findings of the paper by Graham et al was that women who had had one or more severely stressful life experiences in the five years after diagnosis had a lower risk of recurrence than those who didn't (hazard ratio 0.52).¹ Using information collected after baseline (diagnosis in this study) in a survival model is fraught with difficulty because collection of that information may not be possible after the event of interest has occurred. Careful interpretation of the results of any such analysis is therefore recommended.

It seems that a mistake in interpretation has occurred in this paper. Women who had a recurrence were not interviewed again more than eight weeks after their recurrence. So, for example, a woman in whom cancer recurred after 12 months would have nearly four years of missing data for the variable “severely stressful life experiences.” It follows that the investigators were more likely to detect stressful life experiences in women who had recurrences later on in the study or not at all. The finding that stressful life experiences were associated with a decreased incidence of recurrence is probably due to this ascertainment bias rather than any real effect.