Erythropoietin (EPO)-mediated mitogenic and anti-apoptotic effects involve all the cells expressing functional receptors for EPO (EPOR), as demonstrated by in vitro and in vivo studies. EPO shows pleiotropic effects and acts as an endogenous mediator of adaptive tissue response to metabolic stress protecting tissues from different injuries. Recently, the EPO/EPOR complex has been identified in several neoplastic cell lines and solid tumours. In this study, the authors investigated the mast cells (MCs) number, distribution and their immunoreactivity for EPOR in normal, dysplastic and neoplastic canine mammary gland. The results showed that MCs were more numerous in displastic glands compared with normal and neoplastic glands. As far as the EPOR immunoreactivity is concerned, we did not observe MCs reaction on cancer, in contrast with previously published data where epithelium of neoplastic gland showed an increase in EPOR expression along with the neoplastic progression. Overall, our results might be suggestive for MCs role in oncogenesis and offer new insight regarding to the expression of EPOR in mammary gland cancer in dog.