Observations on wet weight, protein and DNA as reference for steroid receptors in malignant mammary tumours.

Estradiol and progesterone receptors were recorded together with DNA and soluble protein per unit wet weight for 235 breast cancer samples. Receptor concentration values per wet weight showed the greatest range of variation. Receptor expressed per unit wet weight, DNA or protein showed good correlation (rs greater than 0.90). In selected cases different information on receptor concentration levels may be obtained depending on the reference parameter used. An overrepresentation was found of tumours with low receptor concentrations or receptors below the level of detection in a subgroup with a low DNA content, indicating the possibility of false low receptor values in this group. High ER and PgR contents were significantly related to high level of tissue DNA. Low or high content of protein was not associated directly with low or high receptor levels. In this respect DNA is superior to wet weight and protein as reference standards for receptor concentration. Further, DNA offers the additional possibility of a rough correction for non-epithelial components of the tumours. A critical dilution of receptors, as shown by low DNA content in some homogenates, was not apparent but cannot be excluded.