To the Editor: The contradictory results presented by Lippman et al.1 and Kiang et al.2 on estrogen receptors and the treatment of breast cancer are not surprising. With the methods used by both groups, the quantity of receptors is expressed per amount of cytosol protein extracted. The number of tumor cells in each sample is, however, unknown. This number certainly varies a great deal; a given weight of medullary carcinoma, for example, may contain 100 times as many tumor cells as a scirrhous carcinoma. A real quantitative estrogen-receptor assay will only be possible and of value for routine clinical use.
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