Menopausal status and cut off levels of steroid receptor ligand binding assays in breast cancer.

494 tubuloductal breast carcinomas obtained at operation were assayed for ER and PgR with short-term ligand incubation and isoelectric focusing. Plasma FSH and E2 concentrations available from 156 of the patients showed strictly premenopausal endocrine conditions in patients 45 years or younger; strictly postmenopausal conditions were found at 55 years or older. ER concentrations were significantly lower in biopsies from premenopausal compared with those from postmenopausal patients. ER concentrations assayed in intervening perimenopausal age period were not statistically different from the premenopausal period. An arbitrarily chosen cut off level to differentiate receptor low from receptor high tumours divided premenopausal assays into two equal parts; those from postmenopausal patients were cut at the second lower percentile. Arbitrary cut off levels ignorant of menopausal status should be replaced by fractionation of low and high receptor tumours on a percentile or quartile basis. Clinically, subgroups or subpopulations of patients should be identified with regard to endocrine and/or receptor status and evaluated separately.