Multicentric aggressive unclassified hematopoietic neoplasm involving the placenta in a pregnant bitch.

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Hematopoietic neoplasms are common in dogs; however, their association with pregnancy has not been previously reported in veterinary medicine. This rare occurrence presents a variety of diagnostic, therapeutic, prognostic, and ethical challenges. We report a case of a 3-year-old pregnant Bernese Mountain Dog diagnosed with multicentric aggressive unclassified hematopoietic cancer associated with paraneoplastic hypercalcemia during pregnancy. The dog died 7 days after diagnosis, and at Day 36 of pregnancy before any treatment decision could be made. Post-mortem evaluation, including histology, immunohistochemistry, and clonality analysis, led to the diagnosis of an unclassified hematopoietic cancer affecting the uterus and placenta, with no evidence of fetal involvement. The placenta likely acted as a barrier, preventing neoplastic involvement of the fetuses. Alternatively, the pregnancy might have been too early for the hematopoietic neoplasm to affect the labyrinth zone of the placenta and the fetuses. The dramatic disease progression could be explained by compromised cell-mediated immunity during pregnancy. This immunodeficient state is induced by embryonic, maternal, and hormonal factors, which suppress the response to mitogens to prevent rejection of the placenta and the conceptuses. Thus, pregnant dogs might exhibit increased vulnerability to cancer and infectious diseases that rely on cell-mediated immunity for host defense.