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Oncology studies often require specially formulated diets to be fed to laboratory animals. To determine the effect of dietary fat on body weight, C3H/HeN mice were carefully assigned by weight into three groups. The first group was fed a high-fat semipurified diet (23% fat by weight) from 21 to 73 days of age then returned to a low-fat semipurified diet (5% fat by weight). A second group was fed the low-fat diet from 21 to 73 days of age, then the high-fat diet until 129 days of age, then returned to the low-fat diet. A final group was fed a 4.5% fat commercial diet for the entire 193-day study. The results showed that the mice fed the semipurified diets did not differ significantly from each other in weight over the course of the study but did differ significantly between 21 and 73 days of age, possibly from a taste preference for the high-fat diet. Mice fed the commercial diet always weighed significantly less. It was estimated that mice fed the commercial diet consumed more food and were less efficient in their food utilization. Mice should be carefully assigned, by weight, into experimental groups, and all groups, including untreated controls, should be fed the same type of diet.

Mammary cancer was induced in 50‐day‐old Sprague‐Dawley rats with either 25 mg/kg body weight of N‐methyl‐N‐nitrosourea (MNU) or 10 mg/rat of dimethyl‐benz(a)anthracene (DMBA). The retinoid N‐(4‐hydroxyphenyl)‐all‐trans‐retinamide (RAHA) was begun in the diet (2.0 mmol/kg diet) of MNU‐induced rats at 21, 48, or 52 days of age, and at 21 or 60 days of age for DMBA ‐induced rats. RAHA was terminated 12–17 weeks postinduction, and the animals were sacrificed at 28 weeks postinduction. Significant inhibition of tumor incidence or multiplicity was found in only one group (rats fed RAHA beginning at 48 days of age). This was not considered sufficient evidence to conclude that short‐term administration of RAHA altered mammary tumor development.

The possible inhibitory effect of vitamin C (sodium ascorbate) on metastases from two transplantable murine tumors was studied. The first murine tumor, colon carcinoma CA-51, was subcutaneously transplanted into male Balb/c mice. Immediately after tumor implantation, the mice were given either 1.0% sodium ascorbate or tap water. Subcutaneous tumors were surgically removed from one half of the animals in each group when the tumors reached a size of 1.5 cm. Results indicated no differences in survival, in the number of mice with metastases, or in the size of metastases between treated and untreated groups. The second murine tumor, lymphosarcoma 6C3HED, was subcutaneously implanted into C3H male and female mice. Sodium ascorbate (1.0% or 3.0%) was administered as above, but surgery was not performed. Again, no significant differences in the number of mice with metastases were observed between treated and untreated groups, with the exception of brain and regional lymph node metastases (enhanced, in males, by ascorbate).