The aim of the present investigation was the evaluation of cost-effectiveness of 
variables used in monitoring patients with inoperable prostate cancer. 
Prostate-specific antigen (PSA), prostatic acid phosphatase (PAP), and 
radionuclide bone scan were considered. The tumor marker positivity was assessed 
according to dynamic criteria (> 50% increase between consecutive samples). 108 
patients entered the study; 72 patients treated with a luteinizing 
hormone-releasing hormone analogue were followed up for periods ranging from 12 
to 64 months. PSA and PAP levels were measured using immunometric assays. Both 
cutoff-based and dynamic, serial sample-based decision criteria were employed. 
With respect to a positive bone scan, PSA showed negative predictive values of 
82 and 77%, respectively, using 4 and 10 ng/ml as cutoff points. Progression of 
the disease to the bone occurred in 20 patients: in 17 PSA was the first 
indicator of progression, in the other 3 PAP anticipated PSA for a very short 
time (3-4 months), which was not of relevance to clinical decisions. PAP is less 
specific and sensitive than PSA; PAP may eventually provide information on 
disease status in a limited percentage of patients with advanced prostate cancer 
treated with androgen ablation, being differently regulated with respect to PSA. 
No increasing PSA profile was detected in patients who responded to the therapy. 
From the results of the present investigation, we draw the following 
conclusions: (1) PSA can be used reliably as a unique tool in the follow-up of 
patients for the early detection of progressive disease, and (2) dynamic 
criteria of evaluation of serial PSA determinations probably provide more 
effective and earlier clinical information.