Tamoxifen as an anti tumor agent: oestrogen binding as a predictive test for tumor response

Rats with growing 7,12 dimethylbenz(α)anthracene (DMBA) induced rat mammary carcinomata were biopsied and oestrogen binding capacity was measured using a Sephadex LH 20 chromatography method. Tumors were measured with calipers and animals were treated for 3 weeks with tamoxifen (50 μg/day, s.c.). Tumor response was determined by the size (cm²) before and after therapy. An increase in tumor regression (ten tumors) was seen with increasing oestrogen binding sites determined by Scatchard analysis (P < 0.01). Thirty tumors were used to determine oestrogen binding with a single dose of [³H] oestradiol. The percentage tumor regression was linearly correlated with oestrogen binding capacity (P < 0.01), although some tumors with high oestrogen binding capacities only partially regressed in response to tamoxifen therapy. The time of the oestrous cycle when biopsy occurred was not a critical factor in determining oestrogen binding for prediction of response. Oestrogen binding was reduced during tamoxifen therapy.