One of the most heated debates in prostate cancer care is around the use of 5-reductase inhibitors (5ARI) like Dutasteride as a third component of a hormone blockade (ADT3). 5-ARIs block the conversion of testosterone to dihydrotestosterone (DHT). DHT is thought to be an extremely powerful “fuel” for the growth of prostate cancer. However, there have never been any studies that show that 5-ARLs actually inhibits prostate cancer progression.

The Therapy Assessed by Rising PSA (TARP) study is an ongoing US and Canadian multicenter trial that investigates the use of dutasteride in combination with bicalutamide in combination with a GnRH analogue (zoladex etc.) to prevent or delay disease progression in men with castrate-refractory prostate cancer (CRPC) after initial androgen deprivation therapy. The trial utilizes a double-blind treatment design with men receiving dutasteride 3.5 mg and bicalutamide 50 mg (ADT3) or placebo and bicalutamide 50 mg (ADT2) once daily

The men participating in the trial all have a rising PSA score while on a GnRH analogue drug. To be included in the trial the men needed to have experienced three rising PSA levels despite taking a GnRH analogue or surgical castration, and no radiographic evidence of metastases (biochemical recurrence). The entry PSA values must be 2.0 ng/ml-20.0 ng/ml and serum testosterone level < 50 ng/dl. The primary endpoint is time to disease progression determined by PSA, or radiographic progression. TARP will be the first study to evaluate the effects of dutasteride and an antiandrogen in patients failing GnRH analogue (ADT3) and help elucidate the potential role of a dual 5ARI in reducing the rate of progression in non-metastatic CRPC. It is assumed that the results of this very important study will not be available until 2013 at the earliest. Reference:
Can J Urol. 2009 Oct;16(5):4806-12.
PubMed Abstract
PMID:19796455

Joel T Nowak MA, MSW