ACTIVATION OF DORMANT CANCER-CELLS IN THE PROSTATES AND SEMINAL-VESICLES OF LOBUND-WISTAR RATS

Lobund-Wistar (L-W) rats are unique in their susceptibility to spontan eous and induced metastasizing adenocarcinomas in the prostate-seminal vesicle (P-SV) complex. Tumors were induced in 70-100% of rats by a c ombination of i.v. inoculated methylnitrosourea (MNU) followed by a se ries of subcutaneous slow-release implants of testosterone propionate (TP). Adenocarcinoma cells initiated by MNU in 3-month-old L-W rats we re activated significantly by implants of the promoter, TP, after inte rvening periods of 3, 6 and 12 months following their exposures to MNU . The longer the time between MNU and TP, the shorter the subsequent l atent period. Control rats inoculated with MNU (without TP) did not de velop tumors during the observation period of 12 months, and their dor mant tumor cells were activated by a single implant of TP, thereby eli citing P-SV tumors.