Response of advanced breast cancer to total endocrine ablation after exacerbation on tamoxifen: results in seven patients and possible mechanism of action.

Usage of tamoxifen in the treatment of advanced breast cancer is increasing and is advocated by some authors as primary therapy in all estrogen receptor positive cancer patients. Tamoxifen is an incomplete estrogen antagonist with partial estrogen agonist activity as well. Tamoxifen-induced exacerbation of breast cancer ("tamoxifen flare") is reported to occur in 4-20% or more of treated patients. Management of this condition has varied from stopping treatment to continued administration or reinstitution of tamoxifen after flare symptoms subside. Responses have occurred in some patients so treated, although the remissions do not appear durable. The seven patients with advanced breast cancer in this report experienced disease exacerbation with tamoxifen therapy. Endocrine ablation afforded all patients excellent pain relief and disease control with prolonged survival in six of the seven. There have been no studies directly examining the disease course in flare patients continuing on tamoxifen. Persistence in treating these patients with an incomplete antagonist-agonist may deprive them of full survival benefit possible through ablative procedures when used in sequential treatment.