The chief use of archival materials is for assessment of current studies and retrospective reviews of past studies. Reviews might serve to confirm the study's original results or suggest expansion of the study to include the use of more sophisticated experimentation methods. For example, in research that was published in both the May 1993 issue of Carcinogenesis and the December 1994 issue of Cancer Research, archival tissue samples were used to perform a retrospective analysis of molecular alterations in methylene chloride-induced lung and liver tumors. Since the time the original study was performed, the carcinogenic effects of methylene chloride had become the subject of closer scrutiny due to recognition of the prevalence of the chemical in industry, food preparation, and agriculture. The new results were used to help interpret the mechanism of tumor induction by methylene chloride, and it was concluded that the compound probably promoted spontaneous background tumors normally observed in the mice.
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Steve McCaw, Image Associates Studies may also be reviewed as scientific advances alert researchers to new factors and events that should be examined. For example, one retrospective study used archived tissues from an earlier study in which o-nitrotoluene, a chemical used in pesticides, pharmaceuticals, and the manufacture of dyes, was determined to induce precancerous liver lesions. The tissues were stained for placental glutathione S-transferase and were monitored for periods of 13 and 26 weeks. The findings demonstrated that, once exposed to o-nitrotoluene, the chemical can be expected to induce hepatocarcinogenesis even if the exposure is stopped. The Carcinogenesis study was designed to evaluate both benign and malignant lung tumors in mice to determine the frequency of K-ras mutations and whether such mutations could be proven to be associated with ozone inhalation.