It is for both staging and improving survival. But whether it does in fact improve survival is controversial, as you can see in the conflicting data in the following two studies:More Extensive Pelvic Lymph Node Dissection Improves Survival in Patients with Node-positive Prostate CancerIs extended pelvic lymph node dissection for prostate cancer the only recommended option? A systematic overview of the literature
Because there are risks of lymphocele and lymphedema, its use remains controversial. It would be a very radical procedure to undertake if its only use were for staging.
NCCN Guidelines said...
Pelvic Lymph Node Dissection:
• An extended PLND will discover metastases approximately twice as often as a limited PLND. Extended PLND provides more complete staging and may cure some men with microscopic metastases; therefore, an extended PLND is preferred when PLND is performed.
• An extended PLND includes removal of all node-bearing tissue from an area bound by the external iliac vein anteriorly, the pelvic sidewall laterally, the bladder wall medially, the floor of the pelvis posteriorly, Cooper's ligament distally, and the internal iliac artery proximally.
• A PLND can be excluded in patients with <2% predicted probability of nodal metastases by nomograms, although some patients with lymph node metastases will be missed.
• PLND can be performed using an open, laparoscopic, or robotic technique.