Background. Influence of tamoxifen treatment on estrogen receptor (ER) and progesterone receptor (PR) levels in human breast cancer has not been fully elucidated in vivo. This problem was studied in 20 postmenopausal patients with ER-positive and PR-positive primary breast cancer.
Each patient underwent two fine-needle aspiration (FNA) biopsies. Between two FNA, 10 patients received no treatment (control group) and the other 10 patients were given tamoxifen (20 mg/day) for an average of 8 days (range, 6-10 days) (TAM group]. Total ER and PR values (cytosolic plus nuclear fraction) in FNA samples were determined by enzyme immunoassay (EIA) for detecting ER and PR regardless of their occupancy with corresponding ligands.
In the control group, no significant difference was found in ER and PR values between the first and second FNA samples. In the TAM group, ER and PR values (mean 2 standard error of the mean [SEMI frnol/ mg DNA) in the second FNA samples were 605 ? 186 and 1130 k 344, respectively, and were significantly higher (P < 0.05) than ER and PR values in the first FNA samples, which were 312 74 and 639 -t 159, respectively. ER and PR values increased by 201 k 27% and 163 2 2370, respectively, on an individual basis after tamoxifen treatment.
These results demonstrated that tamoxifen up-regulates ER and PR in human breast cancer.