CD47 in canine round-cell tumors: an explorative flow cytometric assessment

It is nowadays well established that CD47 protein, a molecule involved in the "don't eat me" signal inhibiting phagocytosis by macrophages, is expressed by various human cells. Several studies reported increased expression in hematological malignancies, and its role in immunotherapy is well known. However, there is currently no information available on its presence in canine neoplasms. The aim of this study is to assess the presence of CD47 on the surface of neoplastic cells in canine round cell tumors using flow cytometry (FC). Samples obtained for diagnostic purposes from dogs diagnosed with mast cell tumors (MCTs), lymphomas or leukemia were included. The surplus material of cellular suspension (from enlarged lymph nodes for lymphoma cases and from the nodule for MCTs) or peripheral blood (for leukemia cases) was tested for CD47 expression via FC. Samples were considered positive if ≥20% of neoplastic cells stained positive for CD47. A total of 120 neoplasms were analyzed, including 85 lymphomas (53 B-cell, 20 T-cell, 12 T-zone Lymphoma), 15 MCTs (12 cutaneous, 2 subcutaneous, 1 not reported) and 20 leukemias (8 chronic lymphocytic, 1 acute lymphoblastic, 1 acute myeloid, 1 chronic myeloid, 9 acute undifferentiated). Positive samples accounted for 27/85 (32%) lymphomas, 15/20 (75%) leukemias, and 12/15 (80%) MCTs. A significant difference in the prevalence of positive samples was found among different diagnoses, with leukemias and MCTs reporting a larger number of positive samples than lymphomas. Conversely, no statistical differences in CD47 expression were found among lymphoma subtypes, between acute and chronic leukemias and among MCT based on grading according to Patnaik/Kiupel system, nor based on lymph node metastatic status. Based on our results, CD47 is expressed by canine round cell tumors and can be assessed via FC, with higher rates observed in leukemias and MCTs compared to lymphomas. The lack of significant differences among subclasses within each diagnostic group should be interpreted with caution, given the limited number of samples included in some groups, possibly influencing the results. As CD47 is widely expressed, it may be included in various panels for immune-checkpoint assessment in round-cell neoplasms, and its prognostic value warrants further investigation.