MSH: A premalignant change arising in the prostatic epithelium, regarded as the most important and most likely precursor of prostatic adenocarcinoma. The neoplasia takes the form of an intra-acinar or ductal proliferation of secretory cells with unequivocal nuclear anaplasia, which corresponds to nuclear grade 2 and 3 invasive prostate cancer.,NCI: Noncancerous growth of cells lining the internal and external surfaces of the prostate gland. Having high-grade PIN may increase the risk of developing prostate cancer.,NCI: A neoplastic proliferation of the epithelial cells that line the acini and the ducts of the prostate gland. The neoplastic epithelial cells are confined within the acini and the ducts and they do not invade the surrounding prostatic stroma. Morphologically, it is classified as low or high grade.