Tamoxifen and interferon-beta for the treatment of metastatic breast cancer.

It has been demonstrated, both in breast cancer cell lines and in metastatic breast cancer patients with cutaneous lesions that could be biopsied, that treatment with interferon beta (IFN-B) can increase expression of both estrogen (ER) and progesterone receptors (PgR). To evaluate the efficacy and toxicity of the combination of IFN and tamoxifen, 33 metastatic breast cancer patients were treated with the following regimen: IFN-B, 6.0 million units intramuscularly IU 3 times a week for two consecutive weeks followed by IFN-B 6.0 million IU im 3 times a week with concomitant tamoxifen 20 mg orally daily. Patients were pre and postmenopausal with median age of 60 years, median ECOG PS of 0, either ER positive or unknown, and had not received prior hormone therapy for metastatic disease. Overall objective response was observed in 9 (27\%) patients. Complete response was observed in 2 cases and partial response in 7 patients. Median duration of response was 7 months (range 2-10). A higher response rate was observed in patients with predominantly soft tissue disease (38\%) compared to patients with either dominant bone (18\%) or visceral lesions (17\%). Toxicity was mild and reversible: low grade fever in 30\% of patients and flu-like symptoms in 9\% of cases. It appears that IFN-B does not improve the efficacy of tamoxifen in an unselected population of metastatic breast cancer.