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Measuring residual estrogen receptor availability during fulvestrant therapy in patients with metastatic breast cancer.

Cancer discovery (2014-11-09)
Michel van Kruchten, Elisabeth G de Vries, Andor W Glaudemans, Meta C van Lanschot, Martijn van Faassen, Ido P Kema, Myles Brown, Carolien P Schröder, Erik F de Vries, Geke A Hospers
ABSTRACT

It is unknown whether the current dose of fulvestrant, an estrogen receptor (ER) antagonist, is sufficient for maximal ER downregulation in patients with metastatic breast cancer. We performed a feasibility study to assess ER availability before and during fulvestrant. Sixteen patients with ER-positive metastatic breast cancer underwent positron emission tomography/computed tomography (PET/CT) at baseline (scan 1), day 28 (scan 2), and day 84 (scan 3) to monitor tumor [(18)F]fluoroestradiol (FES) uptake. Incomplete reduction in ER availability was predefined as <75% decrease in median tumor FES uptake and a residual standardized uptake value (SUVmax) of ≥1.5. In total, 131 FES-positive lesions were identified (median SUVmax of 2.9; range, 1.7-6.5). The median change in patients during fulvestrant treatment was -85% at scan 2, but varied widely (-99% to +60%). Fulvestrant reduced tumor FES uptake incompletely at scan 2 in 6 (38%) of the 16 patients, which was associated with early progression. Serial imaging of tumor estrogen uptake by FES-PET can give insight into the dose needed for ER antagonists to completely abolish ER. FES-PET showed significant residual ER availability in tumors during fulvestrant therapy in 38% of patients, which was associated with early progression.

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Sigma-Aldrich
Tantalum(V) ethoxide, 99.98% trace metals basis
Tantalum(V) ethoxide, packaged for use in deposition systems