tokens: In groups given 2 % BHA , although marked hyperplastic changes of the forestomach epithelium were observed in all animals , co - administration of 0 . 25 % RA significantly ( P less than 0 . 05 ) increased the incidence of forestomach tumors ( squamous cell papilloma and carcinoma ) to 60 % ( 9 / 15 , 2 rats with carcinoma ) from 15 % ( 3 / 20 , one rat with carcinoma ) in the group given RA - free water .