Putative premalignant changes in the prostate have been recognized for a number of years. A variety of synonyms have been given to the most commonly described lesion, characterized by proliferation and dysplasia of the normal two cell layers lining prostatic acini and ductules; prostatic intraepithelial neoplasia (PIN) is the term most often used.
A premalignant prostatic lesion should have morphologicfeatures similarto invasive carcinoma (CA), a spatial association with microinvasive cancer arising from the lesion, and should occur at a greater frequency, severity and extent in organs harboring CA. Most definitively, progression from the premalignant lesion into CA should be observed overtime. PIN fulfills all but the last of these requirements.
High grade PIN is cytologically indistinguishable from prostate carcinoma (CAP). The major differentiating feature between PIN and CAP is the presence, although frequently disrupted, of the basal cell layer in the former. We have studied the basal cell layer in PIN using antibodies to high molecular weight cytokeratins and have found a correlation between PIN grade and the percent disruption of the basal cell layer. The cells making up PIN are phenotypically similarto those of CAP. We have used a variety of markers including cytokeratins, vimentin and the lectin Ulex euroapaeus to demonstrate this similarity. Additionally, we and others have noted decreased PIN immunoreactivity with antibodies directed against prostate specific antigen (PSA) and prostatic acid phosphatase. Other investigators have noted additional phenotypic similarities between PIN and CAP, including the ABH and Lewis antigens. PIN incidence and grade correlate well with the presence of CAP elsewhere in the prostate. In fact, we have noted PIN in all cases of peripheral zone CAP in which radical prostatectomy specimenswere available for review. Thedefinitive requirement for apremalignant lesion is that it undergoes invasion over time. This requirement has not been satisfied with PIN because it is impossible to serially biopsy the same acinar-ductule system on separate occasions.
The clinical importance of PIN follows from three primary observations. We and others have demonstrated that PIN may be associated with elevated serum PSA levels. On transrectal ultrasound of the prostate (the optimum imaging modality for this organ) PIN may appear to give rise to a hypoechoic lesion similar to the most common presentation for CAP. Finally, we have noted that, when PIN is detected on a prostate biopsy, there is a very high incidence of CAP on a repeat biopsy. It would thus appear that PIN represents a major premalignant lesion in the human prostate. The potential for strategies of chemoprevention to inhibit furthertransformationor progression of PIN into invasive carcinoma seems tenable andworthy of further investigation. o 1992 Wiiey-Liss, Inc