Tamoxifen-induced tumor stimulation and withdrawal response.

A postmenopausal breast cancer patient with a measurable lung metastasis was treated with tamoxifen. The tumor doubling time of the pulmonary lesion was 140 days during spontaneous growth and 52 days during tamoxifen therapy, an almost threefold increase in tumor growth rate. This stimulation persisted fro 1 month after discontinuation of tamoxifen and was followed thereafter by a withdrawal regression lasting greater than 6 months. Awareness of the possible tumor growth enhancement with tamoxifen is of importance especially in view of its prolonged activity. Hormone withdrawal regression may occur following tamoxifen therapy, and a sufficient time interval should therefore elapse between cessation of tamoxifen and initiation of other therapeutic modalities.