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

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

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

84 Citations (Scopus)


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 = 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.

SIGNIFICANCE: 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. (C)2014 AACR.

Original languageEnglish
Pages (from-to)72-81
Number of pages10
JournalCancer discovery
Issue number1
Publication statusPublished - Jan-2015


  • PET
  • MG

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