Improved discrimination of prostate cancer and benign prostatic hyperplasia by means of the quotient of free and total PSA.

Abstract

The value of t-PSA (total prostate specific antigen) and of the quotient of free and t-PSA (% f-PSA) for the discrimination of BPH (benign prostatic hyperplasia) and PC (prostate cancer) as well as possible influencing factors were subject to examination under study conditions. The sera of 210 patients (131 BPH, 79 PC patients) were examined by means of the Immulite test; thereof 76 male patients (47 BPH, 29 PC patients) were found to have a t-PSA-value between 4 and 10 ng/ml (grey area). Apart from the age and the findings of rectal digital examination, we recorded the prostate volume, indications of non-specific increases in PSA and for PC patients also the TNM-G stage. For patients with prostate cancer the quotient of f- and t-PSA was significantly lower (median: 0.08) than compared to patients with BPH (median: 0.22) (p<0.001). Also in the grey area the quotient was significantly lower in patients with malignant diagnosis (median: 0.12) than for patients with a non-malignant diagnosis (median: 0.21) (p<0.001). ROC curves were prepared in order to compare the capability of discrimination of the two parameters. At this point, the better discrimination potential of the quotient in the grey area became evident. Due to the fact that priority was given to the detection of carcinoma, the threshold value was defined at a level at which high sensitivity (90%) is existent in combination with an acceptable specificity (approx. 50%). The resultant values are for the total PSA area 0.21, for the grey area 0.19 as a cut-off. Neither the age, nor the prostate volume, nor urinary tract infections had any influence upon the quotient. There was also no correlation between the stage or the grading of the tumour and the percentage of the f-PSA. The quotient alleviates the discrimination between BPH and PC, in particular in the diagnostically problematic grey area. Thus, it can serve as an aid for the decision "biopsy or re-biopsy". As there is currently no standardized method for the application of % f-PSA, there is a requirement for further examination under homogeneous criteria.