2226 - Spatial-Temporal Change in Quantitative Total Bone Imaging (QTBI) and Circulating Tumor Cells (CTCs) in Metastatic Castration-Resistant Prostate Cancer (mCRPC) Treated With Enzalutamide (ENZA)

Background

We report secondary and exploratory analysis with ¹⁸F-NaF PET/CT and CTCs to determine how tumour burden and RNA expression of androgen receptor (AR) splice variants and neuroendocrine (NE) features predict duration of treatment (DoTx) with ENZA.

Methods

Men with progressive mCRPC with ≥ 2 lesions on bone scintigraphy were enrolled and treated with ENZA 160 mg daily at 3 US sites. ¹⁸F-NaF PET/CT scans were obtained at baseline (BL) (PET1), week 13 (PET2), and at the time of PSA progression (per PCWG2 criteria), standard radiographic or clinical progression, or at 2 years without progression (PET3) using QTBI. CTCs were obtained at BL and at PET3. PSA decline and DoTx were compared with BL QTBI, CTC metrics, and change in QTBI.

Results

23 men (median age, 72 years [range, 51-93]; median PSA, 20.5 ng/mL [range, 3.9-133.6]) were enrolled; 22 of which completed planned imaging. The mean number of bone lesions on PET1 was 58 (range 9-168), with a median total standardized uptake value (SUV_total) of 3886.5 (range 506.7-22852.8). DoTx ranged from 1.4 to 31.8+ mo. In general, SUV metrics decreased while on ENZA (PET2) and increased by PET3. Change in lesion heterogeneity (PET1 to PET3) was the most significant predictor of time to PSA progression (hazard ratio, 3.88; 95% confidence interval, 1.24-12.1). ARV7/9 was found in CTCs in 3/20 men and NE features were found in 4/20 men at BL and in 4/19 and in 11/19 men, respectively, at PET3.

Conclusions

Although PSA response with ENZA is high, DoTx is variable. SUV_total at BL did not correlate with DoTx; however, decrease in SUV_total/mean was associated with increased DoTx, with less heterogeneity correlating with a longer time to PSA progression. ARV7/9 or NE expression in CTCs did not predict lack of benefit from ENZA; however, at the time of progression, the observed increase in ARV7/9 and NE expression are consistent with tumor evolution to more aggressive phenotypes. While BL heterogeneity may be prognostic, it may not predict response or DoTx. Assessing response heterogeneity may predict response duration, thus, should be explored as a possible surrogate of benefit in future studies.

Clinical trial identification

NCT02384382.

Editorial acknowledgement

Medical writing and editorial assistance funded by Pfizer Inc. and Astellas Pharma, Inc. was provided by Stephanie Vadasz, PhD, and Michele Salernitano from Ashfield Healthcare Communications.

Legal entity responsible for the study

Pfizer Inc. and Astellas Pharma, Inc.

Funding

Pfizer Inc. and Astellas Pharma, Inc.

Disclosure

G. Liu: Leadership role, Shareholder / Stockholder / Stock options, Employee: AIQ Solutions; Advisory / Consultancy, Research grant / Funding (self), Research grant / Funding (institution): Novartis; Advisory / Consultancy: Exelixis; Advisory / Consultancy, Research grant / Funding (self), Research grant / Funding (institution): Janssen; Advisory / Consultancy, Research grant / Funding (self), Research grant / Funding (institution): TRACON Pharma; Research grant / Funding (self), Research grant / Funding (institution): Madison Vaccines Inc.; Research grant / Funding (self), Research grant / Funding (institution): Pfizer Inc. C.E. Kyriakopoulos: Advisory / Consultancy, Travel / Accommodation / Expenses: Exelixis; Speaker Bureau / Expert testimony: The France Foundation; Research grant / Funding (self), Research grant / Funding (institution): Sanofi. J.M. Lang: Shareholder / Stockholder / Stock options, Licensing / Royalties, I am listed on the patent on a technology for rare cell capture and analysis. This technology has been licensed by Salus Discovery, LLC though no commercial products are available: Salus Discovery; Advisory / Consultancy: Sanofi; Research grant / Funding (institution): Agensys; Research grant / Funding (institution): Pfizer Inc.; Research grant / Funding (institution): Novartis. E.I. Heath: Advisory / Consultancy, Research grant / Funding (institution): Agensys; Honoraria (self), Speaker Bureau / Expert testimony: Sanofi; Honoraria (self): Bayer; Honoraria (self), Research grant / Funding (institution): Dendreon; Honoraria (self), Research grant / Funding (institution): Seattle Genetics; Research grant / Funding (institution): Tokai Pharmaceuticals; Research grant / Funding (institution): Genentech/Roche; Research grant / Funding (institution): Millennium; Research grant / Funding (institution): Celldex; Research grant / Funding (institution): Inovio Pharmaceuticals; Research grant / Funding (institution): Celgene; Research grant / Funding (institution): Zenith Epigenetics; Research grant / Funding (institution): Merck; Research grant / Funding (institution): AstraZeneca; Research grant / Funding (institution): Esanik; Research grant / Funding (institution): Oncolys BioPharma; Research grant / Funding (institution): CureMeta; Research grant / Funding (institution): Bristol-Myers Squibb; Research grant / Funding (institution): eFFECTOR Therapeutics; Research grant / Funding (institution): Fortis. S. Perlman: Research grant / Funding (institution): GE Healthcare Progenics; Advisory / Consultancy: Pfizer Inc. T. Mayer: Advisory / Consultancy: Beacon Biosciences/ICON Medical; Honoraria (self): Novartis; Honoraria (self): AstraZeneca; Research grant / Funding (institution): Sotio; Research grant / Funding (institution): Merck; Research grant / Funding (self): Pfizer Inc. K. Modelska: Travel / Accommodation / Expenses, Shareholder / Stockholder / Stock options, Employee: Pfizer Inc. A. Porcari: Travel / Accommodation / Expenses, Shareholder / Stockholder / Stock options, Employee: Pfizer Inc. W. Duggan: Travel / Accommodation / Expenses, Shareholder / Stockholder / Stock options, Employee: Pfizer Inc. R. Jeraj: Licensing / Royalties, Patents: Wisconsin Alumni Research Foundation; Shareholder / Stockholder / Stock options: AIQ Solutions; Research grant / Funding (institution): GE Healthcare. All other authors have declared no conflicts of interest.