Abstract 679P
Background
The backbone therapy for mCSPC is androgen deprivation therapy (ADT). Since 2014, we have learned that adding docetaxel (DOC) or novel hormonal therapies (NHT) to ADT improves survival over ADT alone. Long-term (≥3 months) use of antiandrogens (AA) plus ADT has also been used for complete androgen blockade. However, real-world evidence on treatment allocation is limited in men with mCSPC.
Methods
Veterans Health Administration (VHA) claims data were used to retrospectively study characteristics and treatment allocation among mCSPC men who initiated either ADT alone or ADT with AA, DOC, or abiraterone (ABI) from 1 April 2014 to 31 March 2018.
Results
The study included 1,553 mCSPC men of which 962 (62%) received ADT only, 384 (25%) received ADT+AA, 118 (8%) received ADT+DOC, and 89 (6%) received ADT+ABI. ADT only patients were generally younger and had lower PSA and alkaline phosphatase levels prior to initiation of therapy. Men treated with ADT+ABI and ADT+DOC were more likely to have metastatic disease in lymph nodes and other sites at treatment initiation (Table). Even among men with respiratory and digestive metastases, the majority received ADT alone (54%). From 2014 to 2017, patients on ADT only (66% to 59%) and ADT+AA (30% to 18%) declined whereas patients using ADT+DOC (2% to 9%) and ADT+ABI (1% to 14%) increased. Multivariable analysis to compare time to metastatic castration-resistant prostate cancer and time to death, using inverse probability of treatment weighting, is ongoing.
Conclusions
Despite our study being conducted in an era of combination therapy for mCSPC, only a small fraction of men in the VHA system received ADT + DOC/ABI, with ADT monotherapy and empirical use of ADT+AA dominating. Future studies are needed to understand whether underuse of modern mCSPC agents will continue in light of new data demonstrating proven survival benefit among all mCSPC men – not just those with high-volume or high-risk mCSPC. Table: 679P
| Patient characteristics prior to treatment initiation | ADT only 962 (62%) | ADT+AA 384 (25%) | ADT+DOC 118 (8%) | ADT+ABI 89 (6%) |
| Median age (years) | 72 | 75 | 67 | 73 |
| Race – White/Black (%) | 64/28 | 72/21 | 71/21 | 63/25 |
| Median prostate-specific antigen value (ng/mL) | 31.5 | 51.3 | 71.6 | 36.4 |
| Median hemoglobin value (g/dL) | 13.0 | 13.2 | 13.9 | 12.5 |
| Median alkaline phosphatase value (IU/L) | 90.0 | 105.0 | 124.5 | 107.0 |
| Site of metastatic diagnosis (%) | ||||
| Lymph nodes | 24 | 17 | 25 | 31 |
| Respiratory and digestive | 6 | 6 | 17 | 4 |
| Other sites (including bone) | 73 | 84 | 90 | 82 |
AA, antiandrogen (bicalutamide, flutamide, nilutamide); ABI, abiraterone; ADT, androgen deprivation therapy; DOC, docetaxel
Clinical trial identification
Editorial acknowledgement
Editorial assistance funded by Pfizer Inc. (New York, NY) and Astellas Pharma, Inc (Northbrook, IL), the co-developers of enzalutamide, was provided by Ira Mills, PhD and Dena McWain from Ashfield Healthcare Communications.
Legal entity responsible for the study
Pfizer Inc. and Astellas Pharma, Inc.
Funding
Pfizer Inc. and Astellas Pharma, Inc.
Disclosure
S.T. Tagawa: Advisory/Consultancy, Research grant/Funding (institution): Astellas Pharma; Advisory/Consultancy, Research grant/Funding (institution): Bayer; Advisory/Consultancy: Tolmar; Advisory/Consultancy, Research grant/Funding (institution): Genentech; Advisory/Consultancy, Research grant/Funding (institution): Endocyte; Advisory/Consultancy, Research grant/Funding (institution), Travel/Accommodation/Expenses: Immunomedics; Advisory/Consultancy, Research grant/Funding (institution): Karyopharm Therapeutics; Advisory/Consultancy, Research grant/Funding (institution): Novartis; Advisory/Consultancy: Genomic Health; Advisory/Consultancy: QED; Advisory/Consultancy, Research grant/Funding (institution): Medivation; Advisory/Consultancy, Research grant/Funding (institution): Janssen; Advisory/Consultancy, Research grant/Funding (institution), Travel/Accommodation/Expenses: Amgen; Advisory/Consultancy: Pfizer Inc.; Advisory/Consultancy: POINT Biopharma; Advisory/Consultancy, Research grant/Funding (institution): Dendreon; Advisory/Consultancy, Research grant/Funding (institution): Abbvie; Advisory/Consultancy, Research grant/Funding (institution), Travel/Accommodation/Expenses: Sanofi; Advisory/Consultancy, Research grant/Funding (institution): Clovis Oncology; Research grant/Funding (institution): Millennium; Research grant/Funding (institution): Merck; Research grant/Funding (institution): Stem CentRx; Research grant/Funding (institution): Rexahn Pharmaceuticals; Research grant/Funding (institution): Inovio Pharmaceuticals; Research grant/Funding (institution): Lilly; Research grant/Funding (institution): Boehringer Ingelheim; Research grant/Funding (institution): Bristol-Myers Squibb; Research grant/Funding (institution): AstraZeneca; Research grant/Funding (institution): AVEO; Research grant/Funding (institution): Exelixis; Research grant/Funding (institution): Progenics; Research grant/Funding (institution): Newlink Genetics; Non-remunerated activity/ies: Telix Pharmaceuticals; Non-remunerated activity/ies: Phosplatin Therapeutics; Non-remunerated activity/ies: ATLAB Pharma. R. Sandin: Shareholder/Stockholder/Stock options, Full/Part-time employment: Pfizer Inc. J. Sah: Full/Part-time employment: STATinMED Research; Research grant/Funding (institution): Pfizer Inc. Q. Mu: Full/Part-time employment: STATinMED Research; Research grant/Funding (institution): Pfizer Inc. S.J. Freedland: Research grant/Funding (institution), Travel/Accommodation/Expenses: Pfizer Inc.; Travel/Accommodation/Expenses: Astellas; Travel/Accommodation/Expenses: Janssen; Travel/Accommodation/Expenses: Bayer; Travel/Accommodation/Expenses: Myovant; Travel/Accommodation/Expenses: AstraZeneca; Travel/Accommodation/Expenses: Merck; Travel/Accommodation/Expenses: Dendreon; Travel/Accommodation/Expenses: Sanofi.