Characterization of spontaneous breast tumor in tree shrews (Tupaia belangeri chinenesis).

Breast cancer is a common malignant tumor. It is essential to develop suitable animal models for discovering novel preventive and therapeutic approaches. Tree shrews (Tupaia belangeri chinensis) have a closer evolutionary relationship with humans than do rodents, which have been widely used in laboratory research. Spontaneous breast tumors were identified in tree shrews in 1960s; however, no detailed studies about tree shrew breast tumors have been conducted to date. Here, we characterized a spontaneous breast tumor from tree shrews by Haematoxylin Eosin (H&E) staining. This tumor was identified as a papillary tumor. Immunohistochemical staining (IHC) for progesterone receptor (PR), Ki-67 and cleaved caspase-3 showed that tumor cells were positive for PR, highly proliferative, and less apoptotic compared to normal breast epithelial cells. Thus, the spontaneous tumor of tree shrew is very close to human papillary tumors in terms of morphology and pathology and we concluded that tree shrew may be a suitable animal model for breast cancer research.