Activation of dormant cancer cells in the prostates and seminal vesicles of Lobund-Wistar rats

Abstract Lobund-Wistar (L-W) rats are unique in their susceptibility to spontaneous and induced metastasizing adenocarcinomas in the prostate-seminal vesicle (P-SV) complex. Tumors were induced in 70–100% of rats by a combination of i.v. inoculated methylnitrosourea (MNU) followed by a series of subcutaneous slow-release implants of testosterone propionate (TP). Adenocarcinoma cells initiated by MNU in 3-month-old L-W rats were activated significantly by implants of the promoter, TP, after intervening periods of 3, 6 and 12 months following their exposures to MNU. The longer the time between MNU and TP, the shorter the subsequent latent period. Control rats inoculated with MNU (without TP) did not develop tumors during the observation period of 12 months, and their dormant tumor cells were activated by a single implant of TP, thereby eliciting P-SV tumors.