Serial [F]-FDHT-PET to predict bicalutamide efficacy in patients with androgen receptor positive metastatic breast cancer.

BACKGROUND

The androgen receptor (AR) is a potential target in metastatic breast cancer (MBC), and 16β-[F]-fluoro-5α-dihydrotestosterone positron emission tomography ([F]-FDHT-PET) can be used for noninvasive visualisation of AR. [F]-FDHT uptake reduction during AR-targeting therapy reflects AR occupancy and might be predictive for treatment response. We assessed the feasibility of [F]-FDHT-PET to detect changes in AR availability during bicalutamide treatment and correlated these changes with treatment response.

PATIENTS AND METHODS

Patients with AR + MBC, regardless of oestrogen receptor status, received an [F]-FDHT-PET at baseline and after 4-6 weeks bicalutamide treatment. Baseline [F]-FDHT uptake was expressed as maximum standardised uptake value. Percentage change in tracer uptake, corrected for background activity (SUV), between baseline and follow-up PET scan (% reduction), was assessed per-patient and lesion. Clinical benefit was determined in accordance with Response Evaluation Criteria in Solid Tumours (RECIST) 1.1 or clinical evaluation (absence of disease progression for ≥24 weeks).

RESULTS

Baseline [F]-FDHT-PET in 21 patients detected 341 of 515 lesions found with standard imaging and 21 new lesions. Follow-up [F]-FDHT-PET was evaluable in 17 patients with 349 lesions, showing a decrease in median SUV from 1.3 to 0.7 per-patient and lesion (P < 0.001). Median % reduction per-patient was -45% and per-lesion -39%. In patients with progressive disease (n = 11), median % reduction was -30% versus -53% for patients who showed clinical benefit (in accordance with RECIST (n = 3) or clinical evaluation (n = 3); P = 0.338).

CONCLUSION

In this feasibility study, a bicalutamide-induced reduction in [F]-FDHT uptake could be detected by follow-up [F]-FDHT-PET in patients with AR + MBC. However, this change could not predict bicalutamide response.

CLINICAL TRIAL INFORMATION

NCT02697032.