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


CONCLUSIONS
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.
Department of Medical Oncology, University of Groningen, University Medical Center Groningen, the Netherlands.
Michel
M
van Kruchten
Department of Medical Oncology, University of Groningen, University Medical Center Groningen, the Netherlands. e.g.e.de.vries@umcg.nl.
Elisabeth G
EG
de Vries
Department of Nuclear Medicine and Molecular Imaging, University of Groningen, University Medical Center Groningen, the Netherlands.
Andor W
AW
Glaudemans
Department of Medical Oncology, University of Groningen, University Medical Center Groningen, the Netherlands.
Meta C
MC
van Lanschot
Department of Laboratory Medicine, University of Groningen, University Medical Center Groningen, the Netherlands.
Martijn
M
van Faassen
Department of Laboratory Medicine, University of Groningen, University Medical Center Groningen, the Netherlands.
Ido P
IP
Kema
Department of Medical Oncology, Dana-Farber Cancer Institute, Harvard Medical School, Boston, Massachusetts.
Myles
M
Brown
Department of Laboratory Medicine, University of Groningen, University Medical Center Groningen, the Netherlands.
Carolien P
CP
Schröder
Department of Nuclear Medicine and Molecular Imaging, University of Groningen, University Medical Center Groningen, the Netherlands.
Erik F
EF
de Vries
Department of Medical Oncology, University of Groningen, University Medical Center Groningen, the Netherlands.
Geke A
GA
Hospers
D000368:Aged; D018931:Antineoplastic Agents, Hormonal / Q000008:administration & dosage / Q000493:pharmacokinetics / Q000627:therapeutic use*; D001943:Breast Neoplasms / Q000175:diagnosis* / Q000188:drug therapy* / Q000473:pathology; D018450:Disease Progression; D004958:Estradiol / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000493:pharmacokinetics / Q000627:therapeutic use; D005260:Female; D000077267:Fulvestrant; D006801:Humans; D008875:Middle Aged; D009362:Neoplasm Metastasis; D049268:Positron-Emission Tomography; D011960:Receptors, Estrogen / Q000037:antagonists & inhibitors*; D013629:Tamoxifen / Q000008:administration & dosage / Q000627:therapeutic use; D014057:Tomography, X-Ray Computed; D016896:Treatment Outcome
D018931:Antineoplastic Agents, Hormonal; D011960:Receptors, Estrogen; D013629:Tamoxifen; D000077267:Fulvestrant; D004958:Estradiol