Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

  • Review Article
  • Published:

Innovations in the systemic therapy of prostate cancer

Abstract

Systemic therapy has become an increasingly important component of treatment of advanced prostate cancer. In the past decade, important innovations have been achieved in the development of novel systemic hormonal therapies for the salvage treatment of metastatic castrate-resistant disease. These improvements have been accompanied by the broadening of potential indications for chemotherapy in castrate-resistant metastatic disease and the use of chemotherapy as an adjunct to the treatment of locally extensive tumors. These changes have begun to lead to improved outcomes, but at the expense of novel patterns of late toxic effects. We review the key steps in the recent evolution of systemic therapy of prostate cancer.

Key Points

  • Docetaxel-based chemotherapy provides a survival benefit for patients with metastatic disease; docetaxel increased median survival from 17.5 months to 19.2 months compared with mitoxantrone

  • Survival for metastatic disease has not improved much in the past decade; however, systemic hormone suppression in association with definitive local therapy has led to improved survival in node-positive patients

  • Although systemic androgen deprivation therapy causes biochemical and clinical castration and suppresses tumor growth, tumors may continue to be stimulated by androgens produced by the adrenal gland or the tumor

  • Abiraterone acetate is a novel hormonal therapy that binds CYP17A1 and irreversibly inhibits this enzyme, which prevents androgen formation; this agent is more specific than other secondary hormonal therapies

  • Abiraterone acetate is currently being evaluated in phase I–II trials; clinical and prostate-specific antigen responses have been reported

  • Many other agents have been tested in castration-resistant prostate cancer, including atrasentan, bevacizumab, sorafenib, erlotinib, gefitinib, calcitriol and doxercalciferol, but their role and utility have not yet been defined

This is a preview of subscription content, access via your institution

Access options

Buy this article

Prices may be subject to local taxes which are calculated during checkout

Similar content being viewed by others

References

  1. Jemal, A. et al. Cancer statistics, 2008. CA Cancer J. Clin. 58, 71–96 (2008).

    PubMed  Google Scholar 

  2. Huggins, C. & Hodges, C. V. Studies on prostatic cancer I: the effect of castration, of estrogen and of androgen injection on serum phosphatases in metastatic carcinoma of the prostate. Cancer Res. 1, 293–297 (1941).

    CAS  Google Scholar 

  3. Berthold, D. R. et al. Docetaxel plus prednisone or mitoxantrone plus prednisone for advanced prostate cancer: updated survival in the TAX 327 study. J. Clin. Oncol. 26, 242–245 (2008).

    CAS  PubMed  Google Scholar 

  4. Petrylak, D. P. et al. Docetaxel and estramustine compared with mitoxantrone and prednisone for advanced refractory prostate cancer. N. Engl. J. Med. 351, 1513–1520 (2004).

    CAS  PubMed  Google Scholar 

  5. Sartor, A. O. et al. Antiandrogen withdrawal in castrate-refractory prostate cancer: a Southwest Oncology Group trial (SWOG 9426). Cancer 112, 2393–2400 (2008).

    CAS  PubMed  PubMed Central  Google Scholar 

  6. Small, E. J. et al. Antiandrogen withdrawal alone or in combination with ketoconazole in androgen-independent prostate cancer patients: a phase III trial (CALGB 9583). J. Clin. Oncol. 22, 1025–1033 (2004).

    CAS  PubMed  Google Scholar 

  7. Tannock, I. F. et al. Docetaxel plus prednisone or mitoxantrone plus prednisone for advanced prostate cancer. N. Engl. J. Med. 351, 1502–1512 (2004).

    CAS  PubMed  Google Scholar 

  8. Trachtenberg, J. & Pont, A. Ketoconazole therapy for advanced prostate cancer. Lancet 2, 433–435 (1984).

    CAS  PubMed  Google Scholar 

  9. Drake, C. G. Immunotherapy for metastatic prostate cancer. Urol. Oncol. 26, 438–444 (2008).

    CAS  PubMed  Google Scholar 

  10. Kiessling, A. et al. Advances in specific immunotherapy for prostate cancer. Eur. Urol. 53, 694–708 (2008).

    CAS  PubMed  Google Scholar 

  11. Loose, D. S., Kan, P. B., Hirst, M. A., Marcus, R. A. & Feldman, D. Ketoconazole blocks adrenal steroidogenesis by inhibiting cytochrome P450-dependent enzymes. J. Clin. Invest. 71, 1495–1499 (1983).

    CAS  PubMed  PubMed Central  Google Scholar 

  12. Ryan, C. J. & Small, E. J. Role of secondary hormonal therapy in the management of recurrent prostate cancer. Urology 62 (Suppl. 1), 87–94 (2003).

    PubMed  Google Scholar 

  13. Montgomery, R. B. et al. Maintenance of intratumoral androgens in metastatic prostate cancer: a mechanism for castration-resistant tumor growth. Cancer Res. 68, 4447–4454 (2008).

    CAS  PubMed  PubMed Central  Google Scholar 

  14. Mostaghel, E. A. et al. Intraprostatic androgens and androgen-regulated gene expression persist after testosterone suppression: therapeutic implications for castration-resistant prostate cancer. Cancer Res. 67, 5033–5041 (2007).

    CAS  PubMed  Google Scholar 

  15. Stigliano, A. et al. Increased metastatic lymph node 64 and CYP17 expression are associated with high stage prostate cancer. J. Endocrinol. 194, 55–61 (2007).

    CAS  PubMed  Google Scholar 

  16. Mohler, J. L. et al. The androgen axis in recurrent prostate cancer. Clin. Cancer Res. 10, 440–448 (2004).

    CAS  PubMed  Google Scholar 

  17. Thomas, L. N. et al. Differential alterations in 5α-reductase type 1 and type 2 levels during development and progression of prostate cancer. Prostate 63, 231–239 (2005).

    CAS  PubMed  Google Scholar 

  18. Hakki, T. & Bernhardt, R. CYP17- and CYP11B-dependent steroid hydroxylases as drug development targets. Pharmacol. Ther. 111, 27–52 (2006).

    CAS  PubMed  Google Scholar 

  19. O'Donnell, A. et al. Hormonal impact of the 17α-hydroxylase/C(17,20)-lyase inhibitor abiraterone acetate (CB7630) in patients with prostate cancer. Br. J. Cancer 90, 2317–2325 (2004).

    CAS  PubMed  PubMed Central  Google Scholar 

  20. Attard, G. et al. Phase I clinical trial of a selective inhibitor of CYP17, abiraterone acetate, confirms that castration-resistant prostate cancer commonly remains hormone driven. J. Clin. Oncol. 26, 4563–4571 (2008).

    CAS  PubMed  Google Scholar 

  21. Ryan, C. et al. Impact of prior ketoconazole therapy on response proportion to abiraterone acetate, a 17-α hydroxylase C17,20-lyase inhibitor in castration resistant prostate cancer (CRPC) [abstract]. J. Clin. Oncol. 26 (Suppl.), a5018 (2008).

    Google Scholar 

  22. Danila, D. C. et al. Abiraterone acetate and prednisone in patients (Pts) with progressive metastatic castration resistant prostate cancer (CRPC) after failure of docetaxel-based chemotherapy [abstract]. J. Clin. Oncol. 26 (Suppl.), a5019 (2008).

    Google Scholar 

  23. De Bono, J. S. et al. Anti-tumor activity of abiraterone acetate (AA), a CYP17 inhibitor of androgen synthesis, in chemotherapy naive and docetaxel pre-treated castration resistant prostate cancer (CRPC) [abstract]. J. Clin. Oncol. 26 (Suppl.), a5005 (2008).

    Google Scholar 

  24. Sternberg, C. N. et al. Phase III trial of satraplatin, an oral platinum plus prednisone vs. prednisone alone in patients with hormone-refractory prostate cancer. Oncology 68, 2–9 (2005).

    CAS  PubMed  Google Scholar 

  25. Sartor, A. O. et al. Satraplatin in patients with advanced hormone-refractory prostate cancer (HRPC): overall survival (OS) results from the phase III satraplatin and prednisone against refractory cancer (SPARC) trial [abstract]. J. Clin. Oncol. 26 (Suppl.), a5003 (2008).

    Google Scholar 

  26. Armstrong, A. J. et al. A phase I–II study of docetaxel and atrasentan in men with castration-resistant metastatic prostate cancer. Clin. Cancer Res. 14, 6270–6276 (2008).

    CAS  PubMed  Google Scholar 

  27. Attia, S. et al. Randomized, double-blinded phase II evaluation of docetaxel with or without doxercalciferol in patients with metastatic, androgen-independent prostate cancer. Clin. Cancer Res. 14, 2437–2443 (2008).

    CAS  PubMed  PubMed Central  Google Scholar 

  28. Boccardo, F. et al. Prednisone plus gefitinib versus prednisone plus placebo in the treatment of hormone-refractory prostate cancer: a randomized phase II trial. Oncology 74, 223–228 (2008).

    CAS  PubMed  Google Scholar 

  29. Chan, J. S. et al. A phase II study of high-dose calcitriol combined with mitoxantrone and prednisone for androgen-independent prostate cancer. BJU Int. 102, 1601–1606 (2008).

    CAS  PubMed  Google Scholar 

  30. Di Lorenzo, G. et al. Combination of bevacizumab and docetaxel in docetaxel-pretreated hormone-refractory prostate cancer: a phase 2 study. Eur. Urol. 54, 1089–1094 (2008).

    CAS  PubMed  Google Scholar 

  31. Gravis, G. et al. Results from a monocentric phase II trial of erlotinib in patients with metastatic prostate cancer. Ann. Oncol. 19, 1624–1628 (2008).

    CAS  PubMed  Google Scholar 

  32. Nelson, J. B. et al. Phase 3, randomized, controlled trial of atrasentan in patients with nonmetastatic, hormone-refractory prostate cancer. Cancer 113, 2478–2487 (2008).

    CAS  PubMed  PubMed Central  Google Scholar 

  33. Chi, K. N. et al. A phase II study of sorafenib in patients with chemo-naive castration-resistant prostate cancer. Ann. Oncol. 19, 746–751 (2008).

    CAS  PubMed  Google Scholar 

  34. Galsky, M. D. et al. Multi-institutional randomized phase II trial of the epothilone B analog ixabepilone (BMS-247550) with or without estramustine phosphate in patients with progressive castrate metastatic prostate cancer. J. Clin. Oncol. 23, 1439–1446 (2005).

    CAS  PubMed  Google Scholar 

  35. Hahn, N. M. et al. A multicenter phase II study of pemetrexed as second-line chemotherapy for the treatment of hormone refractory prostate cancer (HRPC); Hoosier Oncology Group GU-0367 [abstract]. J. Clin. Oncol. 26 (Suppl.), a16019 (2008).

    Google Scholar 

  36. Hussain, A. et al. A phase IIa trial of weekly EPO906 in patients with hormone-refractory prostate cancer (HRPC) [abstract]. J. Clin. Oncol. 22 (Suppl.), a4563 (2004).

    Google Scholar 

  37. Lin, A. M. et al. Clinical outcome of taxane-resistant (TR) hormone refractory prostate cancer (HRPC) paients (pts) treated with subsequent chemotherapy (ixabepilone (Ix) or mitoxantrone/prednisone (MP) [abstract]. J. Clin. Oncol. 24 (Suppl.), a4558 (2006).

    Google Scholar 

  38. Saad, F. et al. Cancer treatment-induced bone loss in breast and prostate cancer. J. Clin. Oncol. 26, 5465–5476 (2008).

    PubMed  Google Scholar 

  39. Bolla, M. et al. Long-term results with immediate androgen suppression and external irradiation in patients with locally advanced prostate cancer (an EORTC study): a phase III randomised trial. Lancet 360, 103–106 (2002).

    CAS  PubMed  Google Scholar 

  40. Bolla, M. et al. Improved survival in patients with locally advanced prostate cancer treated with radiotherapy and goserelin. N. Engl. J. Med. 337, 295–300 (1997).

    CAS  Google Scholar 

  41. Pilepich, M. V. et al. Phase III radiation therapy oncology group (RTOG) trial 86–10 of androgen deprivation adjuvant to definitive radiotherapy in locally advanced carcinoma of the prostate. Int. J. Radiat. Oncol. Biol. Phys. 50, 1243–1252 (2001).

    CAS  PubMed  Google Scholar 

  42. Roach, M. 3rd et al. Short-term neoadjuvant androgen deprivation therapy and external-beam radiotherapy for locally advanced prostate cancer: long-term results of RTOG 8610. J. Clin. Oncol. 26, 585–591 (2008).

    PubMed  Google Scholar 

  43. Kelly, W. K. et al. Multicenter phase 2 study of neoadjuvant paclitaxel, estramustine phosphate, and carboplatin plus androgen deprivation before radiation therapy in patients with unfavorable-risk localized prostate cancer: results of Cancer and Leukemia Group B 99811. Cancer 113, 3137–3145 (2008).

    CAS  PubMed  Google Scholar 

  44. Klotz, L. H. et al. Long-term follow-up of a randomized trial of 0 versus 3 months of neoadjuvant androgen ablation before radical prostatectomy. J. Urol. 170, 791–794 (2003).

    CAS  PubMed  Google Scholar 

  45. Soloway, M. S. et al. Neoadjuvant androgen ablation before radical prostatectomy in cT2bNxM0 prostate cancer: 5-year results. J. Urol. 167, 112–116 (2002).

    PubMed  Google Scholar 

  46. Kang, T. Y. et al. Functional heterogeneity of prostatic intraepithelial neoplasia: the duration of hormonal therapy influences the response. BJU Int. 99, 1024–1027 (2007).

    PubMed  Google Scholar 

  47. Dreicer, R. et al. Phase II trial of neoadjuvant docetaxel before radical prostatectomy for locally advanced prostate cancer. Urology 63, 1138–1142 (2004).

    PubMed  Google Scholar 

  48. Febbo, P. G. et al. Neoadjuvant docetaxel before radical prostatectomy in patients with high-risk localized prostate cancer. Clin. Cancer Res. 11, 5233–5240 (2005).

    CAS  PubMed  Google Scholar 

  49. Friedman, J. et al. Neoadjuvant docetaxel and capecitabine in patients with high risk prostate cancer. J. Urol. 179, 911–916 (2008).

    CAS  PubMed  PubMed Central  Google Scholar 

  50. Garcia, J. A. et al. Clinical and biological effects of neoadjuvant sargramostim and thalidomide in patients with locally advanced prostate carcinoma. Clin. Cancer Res. 14, 3052–3059 (2008).

    CAS  PubMed  Google Scholar 

  51. Shepard, D. R. et al. Phase II trial of neoadjuvant nab-paclitaxel in high-risk patients with prostate cancer undergoing radical prostatectomy. J. Urol. 181, 1672–1677 (2009).

    CAS  PubMed  Google Scholar 

  52. Hussain, M. et al. Neoadjuvant docetaxel and estramustine chemotherapy in high-risk/locally advanced prostate cancer. Urology 61, 774–780 (2003).

    PubMed  Google Scholar 

  53. Chi, K. N. et al. Multicenter phase II study of combined neoadjuvant docetaxel and hormone therapy before radical prostatectomy for patients with high risk localized prostate cancer. J. Urol. 180, 565–570 (2008).

    CAS  PubMed  Google Scholar 

  54. Prayer-Galetti, T. et al. Long-term follow-up of a neoadjuvant chemohormonal taxane-based phase II trial before radical prostatectomy in patients with non-metastatic high-risk prostate cancer. BJU Int. 100, 274–280 (2007).

    CAS  PubMed  Google Scholar 

  55. Sella, A. et al. Neoadjuvant chemohormonal therapy in poor-prognosis localized prostate cancer. Urology 71, 323–327 (2008).

    PubMed  Google Scholar 

  56. Eastham, J. A., Kelly, W. K., Grossfeld, G. D. & Small, E. J. Cancer and Leukemia Group B (CALGB) 90203: a randomized phase 3 study of radical prostatectomy alone versus estramustine and docetaxel before radical prostatectomy for patients with high-risk localized disease. Urology 62 (Suppl. 1), 55–62 (2003).

    PubMed  Google Scholar 

  57. Pilepich, M. V. et al. Phase III trial of androgen suppression using goserelin in unfavorable-prognosis carcinoma of the prostate treated with definitive radiotherapy: report of Radiation Therapy Oncology Group Protocol 85–31. J. Clin. Oncol. 15, 1013–1021 (1997).

    CAS  PubMed  Google Scholar 

  58. Messing, E. M. et al. Immediate hormonal therapy compared with observation after radical prostatectomy and pelvic lymphadenectomy in men with node-positive prostate cancer. N. Engl. J. Med. 341, 1781–1788 (1999).

    CAS  Google Scholar 

  59. Messing, E. M. et al. Immediate versus deferred androgen deprivation treatment in patients with node-positive prostate cancer after radical prostatectomy and pelvic lymphadenectomy. Lancet Oncol. 7, 472–479 (2006).

    CAS  PubMed  Google Scholar 

  60. Hanks, G. E. et al. Phase III trial of long-term adjuvant androgen deprivation after neoadjuvant hormonal cytoreduction and radiotherapy in locally advanced carcinoma of the prostate: the Radiation Therapy Oncology Group Protocol 92–02. J. Clin. Oncol. 21, 3972–3978 (2003).

    CAS  PubMed  Google Scholar 

  61. Kibel, A. S. et al. Adjuvant weekly docetaxel for patients with high risk prostate cancer after radical prostatectomy: a multi-institutional pilot study. J. Urol. 177, 1777–1781 (2007).

    CAS  PubMed  Google Scholar 

  62. Flaig, T. W. et al. Randomization reveals unexpected acute leukemias in Southwest Oncology Group prostate cancer trial. J. Clin. Oncol. 26, 1532–1536 (2008).

    CAS  PubMed  Google Scholar 

  63. Rosenthal, S. A. et al. Phase III multi-institutional trial of adjuvant chemotherapy with paclitaxel, estramustine, and oral etoposide combined with long-term androgen suppression therapy and radiotherapy versus long-term androgen suppression plus radiotherapy alone for high-risk prostate cancer: preliminary toxicity analysis of RTOG 99–02. Int. J. Radiat. Oncol. Biol. Phys. 73, 672–678 (2009).

    CAS  PubMed  Google Scholar 

  64. Le Deley, M. C. et al. Anthracyclines, mitoxantrone, radiotherapy, and granulocyte colony-stimulating factor: risk factors for leukemia and myelodysplastic syndrome after breast cancer. J. Clin. Oncol. 25, 292–300 (2007).

    CAS  PubMed  Google Scholar 

  65. Lu-Yao, G., Stukel, T. A. & Yao, S. L. Changing patterns in competing causes of death in men with prostate cancer: a population based study. J. Urol. 171, 2285–2290 (2004).

    PubMed  Google Scholar 

  66. Basaria, S. Androgen deprivation therapy, insulin resistance and cardiovascular mortality: an inconvenient truth. J. Androl. 29, 534–539 (2008).

    PubMed  Google Scholar 

  67. Basaria, S. et al. Long-term effects of androgen deprivation therapy in prostate cancer patients. Clin. Endocrinol. (Oxf.) 56, 779–786 (2002).

    CAS  Google Scholar 

  68. Basaria, S., Muller, D. C., Carducci, M. A., Egan, J. & Dobs, A. S. Hyperglycemia and insulin resistance in men with prostate carcinoma who receive androgen-deprivation therapy. Cancer 106, 581–588 (2006).

    CAS  PubMed  Google Scholar 

  69. Braga-Basaria, M. et al. Metabolic syndrome in men with prostate cancer undergoing long-term androgen-deprivation therapy. J. Clin. Oncol. 24, 3979–3983 (2006).

    PubMed  Google Scholar 

  70. Bylow, K. et al. Falls and physical performance deficits in older patients with prostate cancer undergoing androgen deprivation therapy. Urology 72, 422–427 (2008).

    PubMed  PubMed Central  Google Scholar 

  71. Derweesh, I. H. et al. Risk of new-onset diabetes mellitus and worsening glycemic variables for established diabetes in men undergoing androgen-deprivation therapy for prostate cancer. BJU Int. 100, 1060–1065 (2007).

    PubMed  Google Scholar 

  72. Efstathiou, J. A. et al. Cardiovascular mortality and duration of androgen deprivation for locally advanced prostate cancer: analysis of RTOG 92–02. Eur. Urol. 54, 816–823 (2008).

    CAS  PubMed  Google Scholar 

  73. Efstathiou, J. A. et al. Cardiovascular mortality after androgen deprivation therapy for locally advanced prostate cancer: RTOG 85–31. J. Clin. Oncol. 27, 92–99 (2009).

    PubMed  Google Scholar 

  74. Keating, N. L., O'Malley, A. J. & Smith, M. R. Diabetes and cardiovascular disease during androgen deprivation therapy for prostate cancer. J. Clin. Oncol. 24, 4448–4456 (2006).

    CAS  PubMed  Google Scholar 

  75. Kiratli, B. J., Srinivas, S., Perkash, I. & Terris, M. K. Progressive decrease in bone density over 10 years of androgen deprivation therapy in patients with prostate cancer. Urology 57, 127–132 (2001).

    CAS  PubMed  Google Scholar 

  76. Lage, M. J., Barber, B. L. & Markus, R. A. Association between androgen-deprivation therapy and incidence of diabetes among males with prostate cancer. Urology 70, 1104–1108 (2007).

    CAS  PubMed  Google Scholar 

  77. Smith, M. R. et al. Diabetes and mortality in men with locally advanced prostate cancer: RTOG 92–02. J. Clin. Oncol. 26, 4333–4339 (2008).

    PubMed  PubMed Central  Google Scholar 

  78. Smith, M. R., Lee, H., Fallon, M. A. & Nathan, D. M. Adipocytokines, obesity, and insulin resistance during combined androgen blockade for prostate cancer. Urology 71, 318–322 (2008).

    PubMed  PubMed Central  Google Scholar 

  79. Smith, M. R., Lee, H. & Nathan, D. M. Insulin sensitivity during combined androgen blockade for prostate cancer. J. Clin. Endocrinol. Metab. 91, 1305–1308 (2006).

    CAS  PubMed  Google Scholar 

  80. Yannucci, J., Manola, J., Garnick, M. B., Bhat, G. & Bubley, G. J. The effect of androgen deprivation therapy on fasting serum lipid and glucose parameters. J. Urol. 176, 520–525 (2006).

    PubMed  Google Scholar 

  81. Satariano, W. A., Ragland, K. E. & van den Eeden, S. K. Cause of death in men diagnosed with prostate carcinoma. Cancer 83, 1180–1188 (1998).

    CAS  PubMed  Google Scholar 

  82. Saigal, C. S. et al. Androgen deprivation therapy increases cardiovascular morbidity in men with prostate cancer. Cancer 110, 1493–1500 (2007).

    CAS  Google Scholar 

  83. D'Amico, A. V. et al. Influence of androgen suppression therapy for prostate cancer on the frequency and timing of fatal myocardial infarctions. J. Clin. Oncol. 25, 2420–2425 (2007).

    CAS  PubMed  Google Scholar 

  84. Tsai, H. K., D'Amico, A. V., Sadetsky, N., Chen, M. H. & Carroll, P. R. Androgen deprivation therapy for localized prostate cancer and the risk of cardiovascular mortality. J. Natl Cancer Inst. 99, 1516–1524 (2007).

    PubMed  Google Scholar 

  85. Cooper, C. S., Campbell, C. & Jhavar, S. Mechanisms of disease: biomarkers and molecular targets from microarray gene expression studies in prostate cancer. Nat. Clin. Pract. Urol. 4, 677–687 (2007).

    CAS  PubMed  Google Scholar 

  86. de Bono, J. S. et al. Circulating tumor cells predict survival benefit from treatment in metastatic castration-resistant prostate cancer. Clin. Cancer Res. 14, 6302–6309 (2008).

    CAS  PubMed  Google Scholar 

Download references

Author information

Authors and Affiliations

Authors

Corresponding author

Correspondence to Derek Raghavan.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Rights and permissions

Reprints and permissions

About this article

Cite this article

Shepard, D., Raghavan, D. Innovations in the systemic therapy of prostate cancer. Nat Rev Clin Oncol 7, 13–21 (2010). https://doi.org/10.1038/nrclinonc.2009.187

Download citation

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1038/nrclinonc.2009.187

This article is cited by

Search

Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing