Prognostic effect of timing of operation in relation to menstrual phase of breast cancer patient--fact or fallacy.

The effects of the timing of operation in relation to menstrual phase and hormone receptor protein positivity and concentration of the 5 year survival of 267 premenopausal women with operable breast cancer were evaluated. The patients were treated in the Tampere University Hospital Area in 1980-87, and information about menstrual cycle was recorded before the operation. Patients operated on during the luteal phase (days 15-32) had a trend towards a better survival rate (80.4%) than those treated in the follicular phase (days 1-14) (75.9%), but the difference did not reach statistical significance (P = 0.079). There was a small difference in the positivity and concentration of hormone receptor proteins, depending on the phase of the menstrual cycle. A more sensitive analysis found a statistically significant linear association between survival and day since last menstrual period (LMP) which was not totally accounted for by the variation in hormone receptor levels during the menstrual cycle or other main prognostic factors (P = 0.018 by Cox's multivariate regression analysis when LMP was used as a continuous variable). One possible mechanism for the effect of timing can be that physiological changes related to different phases of menstrual cycle unfavourably affect the quality of diagnostic and/or treatment procedures. Variation in the lag between the diagnostic confirmation and the operation of the patient affects the evaluation of such an effect and may account for the inconsistent results reported so far.