Extramedullary hematopoiesis in a case of benign mixed mammary tumor in a female dog: cytological and histopathological assessment

Hematopoietic stem cells were found in a benign mixed mammary tumor of a 7-year-old female mongrel dog that presents a nodule in the left inguinal mammary gland. The patient did not have any hematological abnormalities. Cytological evaluation demonstrated two distinct cell populations, composed of either epithelial or mesenchymal cells, sometimes associated with a fibrillar acidophilic matrix, apart from megakaryocytes, osteoclasts, metarubricytes, prorubricytes, rubricytes, rubriblasts, promyelocytes, myeloblasts. Histological examination confirmed the presence of an active hematopoietic bone marrow within the bone tissue of a benign mammary mixed tumor.EMH is a rare condition described in veterinary medicine that can be associated with mammary mixed tumors. It's detection can be associated with several neoplastic and non-neoplastic mammary lesions, i.e. osteosarcomas, mixed tumors and bone metaplasia.Hematopoiesis in the adult animal is restricted to the marrow cavity of flat bones and long bones epiphysis [1]. Thus, extramedullary hematopoiesis (EMH) is defined as the presence of hematopoietic stem cells such as erythroid and myeloid lineage plus megakaryocytes in extramedullary sites and is usually associated with either bone marrow or hematological disorders [1-4]. Despite the fact that extramedullary hematopoieses can occur in any organ, it is more frequently seen in liver, spleen and lymph nodes [3-8].Mammary EMH is a rare condition and it is generally associated with non-neoplastic hematopoietic masses in both woman and bitches. However, the presence of hematopoietic activity can also be seen as an incidental finding associated with mammary neoplasia [2,4,9-12].Cytological examination has been used since the 60's to investigate mammary lesions in women, and it is nowadays largely accepted as a screening test for such lesions in veterinary medicine. It is a minimally invasive and low cost diagnostic method which allows differentiation between non-neoplastic a