Additive antitumor effect of concurrent treatment of 4-hydroxy tamoxifen with 5-fluorouracil but not with doxorubicin in estrogen receptor-positive breast cancer cells.

Purpose The sequential addition of tamoxifen (TAM) to chemotherapy seems superior to its concurrent addition in patients with breast cancer. This study was conducted to clarify the hypothesis that there are differential interactions among TAM and chemotherapeutic agents.