CIRCULATING SPECIFIC PROSTATE ANTIGEN IN BENIGN HYPERTROPHY OR LOCALIZED CANCER OF THE PROSTATE

In benign hypertrophy of the prostate (88 patients) there is a good correlation between the circulating specific prostate antigen (SPA) and the size of the prostate or of the adenoma. This correlation disappears with an adenocarcinoma where tumor volume increases (46 patients). Used as a screeniny test for cancer, serum levels of SPA, with a threshold value of 2.5 ng/ml, has a 91 per cent sensitivity and a 37 per cent specificity. At 15 ng/ml the sensitivity is 50 per cent and the specificity is 85 per cent. Alone, the SPA level is a poor diagnostic tool: using the low threshold (2.5 ng/ml) leads to needle biopsy in most all benign hypertrophies; with the high threshold (15-23 ng/ml), 50 per cent of the localized cancers go undetected. However, for a level greater than 15 ng/ml, SPA is an arguement strongly suggesting prostate adenocarcinoma. The capacity of benign hypertrophy of the prostate to "secrete" SPA is 5 times greater than the normal peripheral prostate; the capacity of cancer is 20 times greater than that of the adenoma. Individual variability in serum levels of SPA, expressed per cm3 of prostate tissue is too great to give a precise interpretation as a function of volume.