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over controls (p < 0.04). Other tumor types showing some significant increase (p < 0.05) in incidence
over controls in some but not all exposure scenarios include lymphosarcomas and Harderian gland
adenomas in male mice, and mammary gland adenocarcinoma, hepatoma, and Harderian gland
adenomas in female mice.
Table 1.
Tumor incidence in CTM mice exposed to drinking water containing 0.4% urethane
(Della Porta et al., 1963a).
A * B C D E control
tumor male female male female male female male female male female male female
type
lung 29/36 53/63 42/56 53/83 58/71 51/68 19/45 26/48 25/30 30/39 2/88 7/99
adenom
a
lymphosarcoma
12/36 17/63 14/56 13/83 14/71 15/68 8/45 7/48 2/30 10/39 4/88 5/99
reticulosarcoma
3/36 4/63 6/56 1/83 8/71 6/68 3/45 2/48 3/30 2/39 0/88 7/99
* Exposure scenarios: A - two 10 day exposures, separated by 10 days; B - one 10 day exposure; C - three 5 day
exposures, separated by 10 days; D - two 5 day exposures, separated by 10 days; E - one 5 day exposure.
Della Porta et al. (1963b) conducted another study similar to that described above, but exposed CTM
mice (75 male and 108 female) to drinking water containing 0.4% urethane for 10 days or two 10-day
periods separated by 10 days. Control animals received plain drinking water (130 males and 120
females). Surviving animals were sacrificed at 75 weeks. The effective group size was considered the
size of the group at the time of appearance of the first malignant lymphoma. Among male and female
mice in both treatment groups, the incidence of malignant lymphoma was elevated over control animals
(15/40 in the 20-day treatment group, 19/61 in the 10-day treatment group, vs. 4/103 controls, p < 10 -
4 by Fisher’s exact test). Among female mice, the incidence of mammary gland tumors was increased
over controls (21/70 in the 20-day treatment group vs. 15/108 controls,p < 0.008; 34/83 in the 10-day
treatment group vs. 15/108 controls, p = 10 -4 ). Other tumors observed included lung adenomas,
mammary carcinomas, liver angiosarcomas, hepatomas, Harderian gland adenomas, and forestomach
and skin papillomas.
Della Porta et al. (1967) exposed four inbred mouse strains (C57BL, C3H, C3Hf, SWR) and one
hybrid mouse strain (B6C3F 1 ) to drinking water containing 0.4% urethane. Five-week old male and
female animals were exposed for 15-20 days in 5- or 10-day periods separated by 10 days, and 10-
day old animals were exposed five times, once every other day. The effective group size for analysis of
tumor incidence was considered the initial number of animals less those dying without tumors before the
25th week for urethane-exposed animals or the 45th week for control animals. The effective group size
ranged from 30 to 158 animals for animals showing significant increases in tumor incidence. Among
male and female B6C3F 1 mice exposed for 10 days, the incidence of Harderian gland tumors (45/51
exposed vs. 3/32 control, males; 44/81 exposed vs. 0/39 control, females; p < 10 -10 , Fisher’s exact
test) and lung adenomas (23/51 exposed vs. 7/32 control, males; 18/81 exposed vs. 4/39 control,
females; p < 0.1) was increased. Among female B6C3F 1 mice alone, the incidence of thymic
lymphosarcoma (10/81 exposed vs. 0/39 control;
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