Tamoxifen was first approved by the FDA in 1978. At that time it was used for women with advanced breast cancer. Subsequently, its use was moved up to the adjuvant setting. Adjuvant means that there was no evidence of breast cancer but that the administration of the agent could diminish recurrence rates of breast cancer. It was recommended for use in women with estrogen receptor cancer.
Estrogen receptor are proteins on the cancer surface and can be detected by pathologists.
Essentially, every woman with breast cancer will know whether their breast cancer is estrogen receptor positive or negative. Statistical analysis was performed to show the importance of this. There were other benefits of Tamoxifen observed in addition to reducing the recurrence rate of breast cancer. Tamoxifen also reduced the occurrence of contralateral breast cancers. This risk factor was based on Gail model.