What duration of androgen deprivation therapy do you use for patients with pN+ prostate cancer undergoing upfront adjuvant RT after a radical prostatectomy and pelvic lymph node dissection?

As @Dr. First Last mentioned, the Messing randomized trial (ECOG 3886) showed that lifelong ADT (vs. observation) improved overall survival in patients with pN+ prostate cancer after radical prostatectomy. This trial provides the only level 1 evidence for this patient population. Therefore, ADT should be considered standard of care.

In practice, however, I believe few medical oncologists actually give lifelong ADT for N+ patients. If these patients are potentially curable, and I believe they are, then lifelong therapy should not be necessary. I believe 2-3 years of ADT would be reasonable, regardless of Gleason score, PSA or pT stage (unless the PSA is really high to make you think that the patient is not curable). 

Adjuvant RT can be offered, adding to this ADT backbone. 

Based on the Messing study, I recommend lifetime androgen deprivation, regardless of other factors. This study showed an overall survival advantage for lifetime ADT.