Application of immunohistologic staining to develop a malignant index to aid in distinguishing benign from malignant prostatic tissue.

The development of antisera with reactivities against intermediate filaments, differentiation antigens, and secretory products has aided in identification and characterization of tissue specimens. Such evaluations may assist pathologists in distinguishing between benign (BPH) and malignant (CAP) tissue of prostatic origin. However, attempts to employ this technique are thwarted by 1) the use of frequently incompletely characterized antisera, 2) the use of both paraffin- and frozen-sectioned materials, and 3) a lack of quantitation in the degree of antisera immunoreactivity. To overcome these shortcomings, a mathematical approach was evaluated using eight BPH and 23 CAP specimens. These were sectioned and stained using commercially prepared antisera against cytokeratin (Cyto P, Cyto M), epithelial membrane antigen (EMA), NK cells (Leu-7), prostatic acid phosphatase (PAP), and prostate specific antigen (PSA). Reactivity was quantitated on a scale of 0-5. Mean values for markers elevated in CAP (relative to BPH) were placed in the numerator; those elevated in BPH (relative to CAP) were placed in the denominator: Malignant index = PSA + EMA + Leu-7 + Cyto M/PAP + Cyto P. This malignant index was significantly greater (P less than .001) in CAP tissues than in BPH regardless of Gleason grade (3.2 +/- 0.9 vs 1.6 +/- 0.9). It was also significantly elevated (3.0 +/- 0.8; P less than .01) in nine specimens representing prostatic atypical hyperplasia. These data suggest that immunohistologic staining may be applied as an aid in distinguishing between BPH and CAP.