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A comparison of the carcinogenic potencies of different substances and an assessment of the risk to exposed people can contribute significantly to the management of carcinogenic hazards including adequate regulatory decisions. A mathematical estimation of the risk caused by a certain height of exposure is usually done under the assumption of a linear dose-response relationship by means of an arithmetical factor which gives the ratio of risk to dose in the low-response range and which has to be found on the basis of epidemiological or experimental data. This work deals with calculations of risk/dose ratios from the data of three carcinogenicity tests by means of statistical methods. The influence of the selection of mathematical model, background assumption and the point of the function chosen for the calculation of the ratio was tested. The results show that an additivity assumption for the background leads to linearity of the curve in the low-response range such that the ratios calculated with different models (multistage, weibull, logit, probit) or for different points of the functions do not differ significantly within the data sets tested. Even under the assumption of independence of the background risk the influence of the model selected is still small if the ratios are calculated for the lowest experimental dose or for an exposure associated risk of 1%. Risk/dose ratios calculated by one of these methods utilize the information of several experimental groups. They seem to be well suited for a direct comparison of the potency of different carcinogens and as a basis for an assessment of the carcinogenic risk to humans, which can serve as a measure of the hazard of a single exposed person or may give an idea about the tumour incidences to be expected within an exposed population.

Among the aminoacyl derivatives of 2,7-diaminofluoren-9-one a few compounds were found capable of inducing interferon in the mouse when administered perorally. One of them, 2,7-bis[(diethylamino)acetylamino]fluoren-9-one exhibited an inducing activity comparable to that of 2,7-bis-(2-diethylaminoethoxy)-fluoren-9-one (tilorone). The synthesis of derivatives of fluorene, fluorenol, fluorenone, diaminobenzophenone, diaminiodiphenylmethane and benzidine, all of them with corresponding side chains, allowed to establish structural requirements for interferon inducing capability.