Inter-site variation of oestrogen receptors in human breast cancers.

When large human breast cancers were assayed for oestrogen receptors at multiple sites, 5-fold differences were found in the numbers of oestrogen receptors, between the site within a tumour. This may result from variations in the cell:stroma ratio from site to site. Such differences could be significant when receptor levels in the tumour are low (less than 50 fmol oestradiol bound mg cytosol protein) since the classification distinction between hormone-sensitive and hormone-insensitive breast cancers is based upon numbers of oestrogen receptors detected by the assay. This problem might be remedied by assessment of the cell:stroma ratio in all assayed tumours, and by the combination of the cytoplasmic oestrogen-receptor assay with other hormone-receptor assays.