T25: a simplified carcinogenic potency index: description of the system and study of correlations between carcinogenic potency and species/site specificity and mutagenicity

Pharmacol Toxicol. 1997 Jun;80(6):272-9. doi: 10.1111/j.1600-0773.1997.tb01973.x.


A simplified carcinogenic potency index, the T25, is proposed as a practical method for the inclusion of potency considerations in carcinogen classification systems. The T25 is the chronic daily dose in mg per kg bodyweight which will give 25% of the animals tumours at a specific tissue site, after correction for spontaneous incidence, within the standard life span of that species. Calculated T25 values of a set of 113 US National Cancer Institute/National Toxicology Program (NC/NTP) carcinogens showed excellent correlation (correlation coefficient 0.96, P < 0.0001) with the carcinogenic potency index TD50 of Peto et al. (1984). The mean of T25 values for 51 transspecies, multiple common site NCI/NTP carcinogens were 10-fold lower than those for 62 NCI/NTP single species, single site carcinogens. For these 113 carcinogens, the mean T25 values were approximately 3-fold lower for agents that were also mutagenic in Salmonella compared to the non-mutagenic agents.

MeSH terms

  • Abdominal Neoplasms / chemically induced
  • Adenocarcinoma, Bronchiolo-Alveolar / chemically induced
  • Animals
  • Butadienes
  • Carcinogenicity Tests / methods*
  • Carcinogens
  • Carcinoma, Hepatocellular / chemically induced
  • Carcinoma, Transitional Cell / chemically induced
  • Chloroform
  • Female
  • Liver Neoplasms, Experimental / chemically induced
  • Lung Neoplasms / chemically induced
  • Male
  • Mesothelioma / chemically induced
  • Mice
  • Mutagenesis*
  • Neoplasms, Experimental / chemically induced
  • Rats
  • Rats, Inbred F344
  • Species Specificity
  • Toluidines
  • Urinary Bladder Neoplasms / chemically induced


  • Butadienes
  • Carcinogens
  • Toluidines
  • Chloroform
  • 2-toluidine
  • 1,3-butadiene