The authors have reinvestigated the phosphohexose isomerase (PHI) serum activity in 60 patients with prostatic hypertrophy and cancer with the enzymatic procedure of Noltman, more accurate and sensitive than the colorimetric method used by Bodansky and other authors. The PHI activity varied from 20 mU to 30 mU in normal subjects, while in patients with prostatic hypertrophy it varied from 60 mU to 80 mU. In prostatic carcinoma it was constantly above 110 mU. In normal subjects and in prostatic cancer, the enzymatic assay values were lower than those reported by Bodansky. In all cases the diagnosis was confirmed by bioptic inspection. An important fact was that extremely high values (not included in the mean) have been found in some patients with widely diffused metastasis. Considering also the few intermediate values which cannot be easily included in the reported groups (between 30 and 50 mU in 1 normal subject, and 2 prostatic hypertrophies; between 70 and 90 mU in 2 prostatic hypertrophies and 3 cancers), the present investigation shows that the enzymatic assay of PHI may be clinically very interesting. It provides selective values for the diagnosis not only between prostatic hypertrophy and cancer but also in cases of hypertrophy with single suspected nests, and, above all, in cancer metastatized. The method is much more worthy, about 90%, than those of serum phosphatases, which reach, by Cavazzana, 75% at least
