Prostatic intraepithelial neoplasia (PIN): morphological clinical significance

Premalignant lesions of the prostate fall into two categories. The first category includes formation of new, usually small, glands which are either abnormally distributed or show minimal nuclear atypia or both. Morphologically, this lesion presents the differential diagnostic alternatives of micro-acinar hyperplasia on the one hand and a low grade micro-acinar cancer on the other. If the presence or absence of nuclear anaplasia or acinar dispersion (i.e., stromal invasion) raises any degree of doubt, atypical glands are diagnosed. This is the category that is considered by some to be the precursor of well differentiated prostate cancer. The second category is prostatic intraepithelial neoplasia (PIN). We have defined PIN as an intra-acinar or ductal proliferation of secretory cells with unequivocal nuclear anaplasia, which corresponds to nuclear grade 2 and 3 invasive prostate cancer. We consider PIN as essentially carcinoma in situ. The lesion designated by some as PIN 1 is classified by us as atypical hyperplasia.