Hello Ali Mussa

For breast cancer induction, it is better to use rat because they are similar to what is seen in human breast cancer, present a high frequency of hormone dependence and show a tumor progression from ductal hyperplasia and ductal carcinoma in situ. These characteristics make them good models to study the development of breast cancer. On the other hand, mice when compared with humans have a low frequency of hormone dependence and show a tumor progression from alveolar hyperplasia.

Currently, there are only two chemical carcinogenic agents (7,12-dimethylbenzantracene (DMBA) and N-methyl-N-nitrosourea (NMU)) that can induce mammary tumors in rats after single dose of carcinogen and that exhibit histopathological characteristics and genetic alterations like those described in humans. The optimal age for carcinogen administration occurs between 45- and 60-days of age, corresponding to the age of rat puberty, which is the stage where a faster expansion of the mammary gland epithelium occurs.

Rat tumors are not extremely invasive beyond the mammary fat pad, have short latency, seldom metastasize and are highly hormone-dependent and therefore are widely used as models of estrogen dependent breast cancers.

On the other hand, most mouse strains are far more resistant than rats to chemical induced mammary gland carcinogenesis, typically requiring multiple doses of carcinogens like DMBA and developing only after a long latency.

So, for breast cancer induction you can go for rat model, and the duration of tumor induction is also relatively shorter in rats compared to mice.

I hope this helps.

Best.

For Breast cancer induction mice are suitable because of mice are smaller in size and the induction period 3 to 4 month.

Mice is best