Immunoreactive human chorionic gonadotrophin (hCG) was found in 9 of 65 surgically removed malignant breast tumours. The concentrations found ranged from 5 to greater than 500 mIU hCG/g tumour. Of the nine, seven extracts were assayed for total protein content; when expressed as mIU/mg extract protein, the hCG concentrations ranged from 0.28 -> 18.2 mIU/mg protein. Comparison of oestrogen receptor and hCG presence in the tumours showed no strong correlation. All tumours in which hCG was detected were shown to be of ductal origin. The hCG was measured by a β-chain specific radioimmunoassay which measures only hCG even in the presence of high levels of other gonadotrophin hormones. In further study of these specimens an immunoperoxidase staining technique was used to stain for hCG in formalin-fixed sections of the same tumours assayed by RIA. This technique confirmed hCG in the positive specimens examined (tissue was available for 7 of the 9 positives) and no significant staining in any negatives. The hCG was shown to be localized within the cytoplasm and on the surface of the malignant cells but not in surrounding normal cells. This intracellular localization demonstrates that the malignant cells may produce hCG, rather than stimulating the pituitary to do so.
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