Rats were weighed weekly and palpated for the presence of mammary tumors.

The exact causes for the development of canine mammary tumors are not fully understood.

Dogs have an overall reported incidence of mammary tumors of 3.4 percent.

The average age of dogs with mammary tumors is ten to eleven years old.

They are the most malignant type of canine mammary tumor.

The molecular carcinogenesis of canine mammary tumors are not completely understand.

Appearance and location of the tumor is enough to identify it as a mammary tumor.

Spayed rats have a decreased risk of developing mammary tumors.

The majority of deaths were caused by neoplasms, mainly mammary tumors.

The groups had 2.84, 3.82, and 5.00 mammary tumors per rat respectively.