Growth of human breast cancers in Peromyscus .

Modeling breast cancer in general and hormone-sensitive breast cancer, in particular in mice, has several limitations. These are related to the inbred nature of laboratory mice, and do not allow adequate appreciation of the contribution of the host's genetic heterogeneity in tumor growth. In addition, the naturally low estrogen levels of mice makes estradiol supplementation obligatory for tumor growth. Here, we show that Peromyscus californicus , following cyclosporine-mediated immunosuppression, supports the growth of both MDA-MB-231 estrogen-independent and MCF7 estrogen receptor-positive breast cancers without exogenous estradiol supplementation. Tumor growth was inhibited by fulvestrant or letrozole, confirming that MCF7 xenografts remain hormone dependent in vivo and suggesting that P. californicus can be used as an alternative to conventional mice for the study of hormone-sensitive breast cancer. The fact that Peromyscus stocks are outbred also facilitates the study of breast cancer in genetically heterogenous populations.