ABSTRACT
Histological examination is the sine qua non for the diagnosis of malignant neoplasia. Although the differential diagnosis between benign and malignant is essentially based on morphological criteria, the need for new methodology capable of resolving the seemingly continuous spectrum of neoplasia into narrow bands of specific histopathologic entities is being increasingly recognized. A number of histochemical and immunohistochemical assays have already been introduced and help to differentiate between various types of neoplasms and their tissue of origin. In particular, immunohistochemical assays are becoming commonplace for the detection of tissue-or tumorspecific antigens in routinely processed biopsies or surgically resected specimens. The practical applications of the concept of tissue-specific antigens are best exemplified by prostatic acid phosphatase (PAP) and the prostatic-specific antigen (PSA). Both substances are localized almost exclusively in the prostatic epithelium and its secretory products and are, therefore, considered markers of prostatic origin. Their presence identifies a cell as prostatic in origin but cannot be used to differentiate between benign and malignant. To date, their major contribution has been the identification of metastatic lesions when the primary source of malignancy is not apparent. This has great clinical relevance as the identification of metastases originating in the prostate results in the patient being given the benefit of specific treatment, including hormonal manipulation.
