High skin tumour initiating activity of the metabolically derived trans-3,4-dihydro-3,4-diol of the carcinogen 15,16-dihydro-11-methylcyclopenta[a]phenanthren-17-one.

Eight main metabolites of the parent carcinogen 15,16-dihydro-11-methylcyclopenta[a]phenanthrene-17-one (I) were assayed for their ability to initiate skin tumours in T.O. mice after topical application in two-stage experiments with croton oil used as the promoter. All were less active than 1 with the exception of the trans-3,4-dihydro-3,4-diol which was more than ten times as active. This diol is therefore confirmed as the proximate carcinogen, a conclusion reached previously on different evidence.