Spontaneous hepatomas in mice inbred from Ha:ICR Swiss stock: effects of sex, cedar shavings in bedding, and immunization with fetal liver or hepatoma cells.

Mice from Ha:ICR noninbred Swiss stock were mated brother X sister for 21--25 generations and then maintained up to the age of 33 months. Hepatomas developed in 62.8% of 86 males autopsied at 349--999 days of age (mean age = 21.1 mo). Of 130 females, 6.9% had hepatomas when autopsied at 328-825 days of age (mean age = 18.7 mo). Hepatoma incidence in males at 18 months of age was not affected by the presence or absence of cedar shavings in the bedding or by immunization of 3-month-old males with 2 weekly inoculations of 150 microgram (protein) sonicate of fetal liver or spontaneous hepatoma cells.