#GU15 - Early radiation response between GnRH agonist versus antagonist combined with radiotherapy in high-risk prostate cancer - Session Highlights

ORLANDO, FL, USA (UroToday.com) - GnRH agonist and GnRH antagonist are two different strategies to provide androgen blockade. Degarelix, a GnRH antagonist, provides a very rapid and sustained androgen blockade while GnRH agonists initially lead to androgen release, followed by a blockade. This group investigated whether high-risk prostate cancer patients could respond differently to radiotherapy + degarelix as compared to radiotherapy + GnRH.

gucancerssympaltThe cohort consisted of 11 patients who underwent degarelix + radiotherapy who were compared to another 19 patients who underwent GnRH agonist +radiotherapy. MRI was performed before the start of hormones and 3 months after the end of radiotherapy. Choline (which represents tumor metabolism) and citrate (which represents healthy prostate metabolism) were quantified with MR spectroscopy and the slopes of gadolinium wash-in (SWI) and wash-out (SWO) were assessed in the peripheral zone, the central gland, and the tumor with DCE-MRI.

There was no difference between the groups with respect to baseline PSA, mean prostate volumes, and the median dose of RT administered. Also, there were no significant differences in the choline, citrate, SWI and SWO in the peripheral zone, central gland, and the tumor. At 3 months, there was no difference between the groups in prostate volume and PSA levels. Citrate levels were significantly decreased with degarelix in the peripheral zone and central zone but not in the tumor. Choline concentrations were similar in both groups in all three locations. There was a trend towards a lower contrast uptake in the tumor with degarelix although not statistically significant.

These results suggest that degarelix combined with radiotherapy offers a significant, early, more profound metabolic atrophy in the prostate, but not in the tumor. Additionally, there is a trend towards lower tumor vascularization with degarelix compared with GnRH agonists. It is yet to be seen if these differences translate into clinical differences.

Presented by Gilles Crehange, Alexandre Cochet, Adele Cueff, Etienne Martin, Philippe Maingon, Francois Brunotte, and Paul M Walker at the 2015 Genitourinary Cancers Symposium - "Integrating Biology Into Patient-Centric Care" - February 26 - 28, 2015 - Rosen Shingle Creek - Orlando, Florida USA

Georges François Leclerc Cancer Center, Dijon, France; Department of Nuclear Medicine, Georges-François Leclerc Cancer Center, Dijon, France; Department of MR Spectroscopy and Nuclear Medicine, University Hospital, Dijon, France

Reported by Mohammed Haseebuddin, MD, medical writer for UroToday.com