Prostatic Localization of Spontaneous Early Invasive Carcinoma in Lobund-Wistar Rats1

Animal models of human prostate cancer are very limited in number but are of obvious importance to develop. Dr. Morris Pollard (M. Pollard, J. NatI.Cancerlust.,51: 1235—1241, 1973)hasreportedthatLobund Wistar rats develop spontaneous metastatic prostatic cancer when they become old (—†̃25%incidence after 25 months). A chemically induced form of the disease has also been described in Lobund-Wistar rats. However, recent reports suggest that most of the chemically induced adenocarcino mas are not prostatic in origin, with most arising in the seminal vesicle, and thereby raise questions about the origin of the spontaneous cancers. We herein report cancer spontaneously arising in the lateral lobes of the prostates in Lobund-Wistar rats. One of 8 rats killed at 16 months of age showed prostatic carcinoma in situ. Two of 39 rats killed at 20 months displayed early invasive adenocarcinomas with no signs of metastases. Because sectioning of the prostates in this study was lhnited to face sections from a single block for each rat, it is highly probable that the true incidence of dysplasias and carcinomas is underestimated by these data. Dysplastic or neoplastic changes were not seen in either the seminal vesicles or other portions of the prostatic complex. The nuclei of adeno carcinoma cells showed less labeling with antibody to the androgen hor mone receptor than did normal cells. These data strongly support the validity of the Pollard model of spontaneous prostate cancer in Lobund Wistar rats.