A pilot study of the effects of short-term tamoxifen therapy on Ki-67 labelling index in women with primary breast cancer

In this study we demonstrate the change in estrogen receptor (ER) level and cell proliferation in human breast cancer after a short-term tamoxifen the rapy. Ten pre and post-treatment breast tumor samples were examined immunoh istochemically using ER and Ki-67 antibodies. Before tamoxifen treatment, s ix (60%) of ten patients were positive for ER. Tamoxifen increased the ER l evel in one patient and decreased the level in 4 patients. There was no sig nificant change in ER level by tamoxifen therapy. On the other hand, Ki-67 labelling index (LI) significantly decreased after tamoxifen treatment. Whe n Ki-67 LI was analyzed according to ER level, there was no difference betw een pre- and post-tamoxifen treatment in ER-negative patients, however, a s ignificant decrease of Ki-67 LI by tamoxifen treatment was seen in ER-posit ive patients. Patients who showed down-regulation of ER expression tended t o show a decrease of Ki-67 LI after tamoxifen therapy. In conclusion, short -term tamoxifen therapy decreased the proliferation of breast cancer, in ER -positive breast tumor samples.