A 6-year-old spayed female Great Dane presented to a medical oncologist with a 2-week history of inappetance, intermittent vomiting, fever, and a non-productive cough. Thoracic radiographs by the rDVM showed an area of consolidation in her right caudal lung lobe so she was initially treated on an out-patient basis with subcutaneous fluids and antibiotics. The patient failed to improve, remained febrile, and became almost completely inappetant. Subsequent radiographs show persistence of the consolidated right caudal lung. Abdominal ultrasound and general lab work were unremarkable except for mild hyperglobulinemia and hypoalbuminemia. The consolidated area of lung can be seen peripherally on ultrasound so was aspirated to obtain a diagnosis.
The slides from the consolidated lung were moderately to highly cellular and consisted of few to many red blood cells and a nucleated cell population predominated by individual round to irregularly- shaped cells with an abundant amount of lightly to moderately basophilic cytoplasm that commonly contains many small clear punctate vacuoles. The nuclei are round to irregularly-shaped with a coarsely- to finely-stippled chromatin pattern and 2-4 prominent nucleoli of variable size and shape. Bi- and multinucleation are commonly noted, including many very large multinucleate giant cells. Anisokaryosis and anisocytosis are marked. Mitotic figures are commonly noted. Leukophagocytosis is occasionally noted. The definitive cytologic diagnosis was histiocytic sarcoma. Representative photos are below.
Canine histiocytic tumors are a very complex group of neoplasms that range from the benign cutaneous histiocytoma to the malignant histiocytic sarcoma complex, with several other histiocytic diseases in between. Within the histiocytic sarcoma complex, there is the solitary histiocytic sarcoma which is typically locally or regionally aggressive, and malignant histiocytosis or disseminated histiocytic sarcoma, which metastasizes beyond regional lymph nodes and commonly infiltrates visceral organs such as liver, spleen, and/or bone marrow. Like the cells in this case, the cytomorphology of neoplastic cells from histiocytic sarcomas are distinctive. In comparison to the more common immature large lymphocytes of high-grade lymphoma, malignant histiocytes from histiocytic sarcomas typically exhibit more extreme pleomorphism with more irregularly-shaped nuclei, more extreme anisokaryosis and anisocytosis, and abundant binucleate and multinucleated cells. The cells also typically have more abundant light gray cytoplasm that can contain vacuoles and may also contain phagocytized erythrocytes or leukocytes. In some cases, differentiating between high-grade lymphoma and histiocytic sarcoma can be more challenging, in which cases immunocytochemical (ICC) or immunohistochemical (IHC) markers must be used to obtain a definitive diagnosis.
At this time, the tumor in this patient is localized to the right caudal lung lobe, but the oncologist is worried other sites of disease may be present. The patient has new onset stridor, therefore there is a concern for metastasis to cervical lymph nodes. The patient also has unexplainable GI signs, inappetance and vomiting, which have improved with her treatment; thus concern exists for other sites of metastasis that were not detected via ultrasound. A few days after receiving doxorubicin, Zometa™ (zoledronic acid), and supportive care, the patient is feeling much better and her hypoalbuminemia is improving.
Submitted by Casey J. LeBlanc, DVM, PhD, DACVP of KDL VetPath – June 201
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