In vivo prediction of response to antiestrogen treatment in estrogen receptor-positive breast cancer.

UNLABELLED In metastatic breast cancer, the estrogen receptor (ER) is a well-known prognostic factor predictive of response to hormonal treatment in most, but not all, patients. Recently, a receptor-specific radioligand for in vivo imaging of the ER in breast cancer patients was developed: (123)I-labeled cis-11beta-methoxy-17alpha-iodovinyl-estradiol (Z-(123)I-MIVE). It showed high sensitivity and specificity for the in vivo detection of ER-positive breast cancer. The aim of this study was to determine whether Z-(123)I-MIVE scintigraphy is able to predict response or resistance to antiestrogen therapy in patients with metastatic ER-positive breast carcinoma. METHODS Twenty-three patients with first metastases of their breast cancer and positive Z-(123)I-MIVE scintigraphy were included and treated with tamoxifen, 40 mg/d. Scintigraphy was repeated, on average, 4 wk later. The results of these scintigraphies were compared with the clinical outcome. RESULTS On baseline scintigraphy, 21 of 23 patients had clear uptake and 2 of 23 patients had faint uptake of Z-(123)I-MIVE. After initiation of antiestrogen treatment, 17 of 21 patients with clear uptake on baseline scintigraphy showed complete blockade of ER activity on the Z-(123)I-MIVE scintigraphy. Four of 21 patients showed mixed or no ER blockade. All patients with faint baseline uptake or mixed or no ER blockade after tamoxifen showed progressive disease despite antiestrogen treatment. Patients with clear baseline uptake and complete ER blockade after tamoxifen had a significantly longer progression-free interval (mean +/- SEM, 14.4 +/- 1.6 vs. 1.8 +/- 0.8 mo; P < 0.01). CONCLUSION Z-(123)I-MIVE scintigraphy seems to be a useful tool to predict response or resistance to antiestrogen treatment in ER-positive metastatic breast cancer patients and to depict nonresponders before the clinical manifestation of progression.