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As many as 30% of men over the age of 55 harbor latent prostate cancers, detectable only at postmortem examination. Greater than 95% of cancers of the prostate are gland-forming adenocarcinomas, which have a predilection for the peripheral zones. The remaining prostate cancers are divided between squamous cell and transitional cell carcinomas (arising from the prostatic ducts), small cell and other neuroendocrine tumors, and rarely, carcinosarcomas. The histologic precursor lesion of prostatic adenocarcinomas is prostatic intraepithelial neoplasia (PIN), which shares not just the cytological features of cancer, but also many of the associated genetic abnormalities. Unlike adenocarcinomas, PIN occurs within preexisting acinar structures, and is divided into low-grade and high-grade variants. The latter is a more reproducible diagnosis and also has a stronger morphologic, genetic and clinical association with prostate cancer. In fact, the presence of isolated high-grade PIN in needle biopsy specimens strongly suggests that there is a co-existing carcinoma in the prostate.
Prostate cancers have been traditionally graded by the Gleason's histologic scoring scheme, that recognizes five grades representing a continuum of architectural patterns of glandular and acini formation. Tumor grades on needle core biopsies are important in guiding management options as well as assessing prognosis in the individual patient. Thus, scores of 2-6 represent the well to moderately differentiated end of the histologic spectrum, while scores of 8-10 constitute poorly differentiated tumors. Tumors with a Gleason's score of 7 occupy an intermediate position not just with regards to the histologic grade, but also biologic behavior. Needless to say, stage of disease is also a critical determinant of prognosis, and disease specific survival decreases progressively from organ-confined cancers to those with regional and subsequent, distant metastases. A variety of "non-traditional" prognostic markers have come recently into vogue as prognostic indicators in prostate cancers. For example DNA aneuploidy in prostate cancers correlates with a higher stage disease and shortened survival. Other studies have focused on the role of MIB-1 labeling index as a measure of proliferation, bcl-2 expression, loss of E-cadherin expression, and abnormal p53 accumulation as prognostic indicators in predicting outcome. The search continues to define the ideal marker(s) that would foretell disease progression and aggressiveness in newly diagnosed prostate cancers. |
