tokens: More than 50 % of Lobund - Wistar ( L - W ) strain rats developed large , palpable prostate adenocarcinomas ( PAs ) following treatments with N - nitroso - N - methylurea ( CAS : 684 - 93 - 5 ) and testosterone propionate [ ( TP ) CAS : 57 - 85 - 2 ] , and most of the tumor - bearing rats manifested metastatic lesions .