Pulmonary histiocytic sarcoma in a rabbit

Disseminated histiocytic sarcoma in a degu (Octodon degus)

A 7-year-and-8-month-old, male degu (Octodon degus) with anorexia, depression, and labored breathing was found to have a thoracic effusion and enlargement of the right testis on radiographic examination. Despite treatment, the animal died. At necropsy, hepatomegaly, splenomegaly, and multifocal nodules on the intestinal serosa and mesentery were observed. Histologically, the foci were densely cellular invasive neoplasms composed of sheets of round to polygonal cells, with occasional multinucleated giant cells. Immunohistochemically, the neoplastic cells were immunopositive for ionized calcium-binding adapter molecule 1, human leukocyte antigen-DR, and CD204. These findings were consistent with disseminated histiocytic sarcoma.

Cutaneous Histiocytic Sarcoma with Giant Cells in a Free-ranging Brush Rabbit (Sylvilagus bachmani)

A cutaneous mass in a free-ranging brush rabbit (Sylvilagus bachmani) was composed of neoplastic spindle to polygonal cells with multinucleated giant cells, which were positive for CD204 and negative for smooth muscle actin and desmin. Histiocytic sarcoma with giant cells was diagnosed; this neoplasm has not been reported previously in free-ranging lagomorphs.

Spontaneous Disseminated Histiocytic Sarcoma in a Bengal Tiger (Panthera tigris tigris)

A 16-year-old, female, captive Bengal tiger (Panthera tigris tigris) had a history of a recurrent subcutaneous mass. After two attempts at surgical removal, euthanasia was elected during the third surgical attempt due to the degree of neoplastic infiltration. At necropsy, a large subcutaneous mass infiltrated the dermis, subcutis and abdominal wall with metastasis to the lungs, spleen and adrenal glands. Microscopically, the neoplasm formed nodules comprising sheets of round cells with large irregular nuclei. Toluidine blue and Giemsa stains were negative. An immunohistochemistry panel revealed membranous and cytoplasmic labelling with ionized calcium-binding adaptor molecule 1 (IBA1), cytoplasmic labelling with vimentin but no labelling with multiple myeloma oncogene 1 (MUM1), CD20 or pancytokeratin markers. Based on the gross distribution and histological and immunohistochemistry features, a diagnosis of disseminated histiocytic sarcoma was made. To the best of our knowledge, this is the first record of disseminated histiocytic sarcoma in a captive Bengal tiger.

Clinicopathologic, immunohistochemical, and ultrastructural features of histiocytic sarcoma in a chinchilla (Chinchilla lanigera)

A 9‐year‐old intact female chinchilla (Chinchilla lanigera) was presented to a referring veterinarian due to small, multiple cervical nodules that had been rapidly increasing in size and number. Cytology of the nodules revealed sheets of pleomorphic round cells that were morphologically most compatible with histiocytic sarcoma. Histologically, the nodules were fairly demarcated, partially infiltrative, densely cellular neoplasm, and was composed of pleomorphic large round cells arranged in sheets. Special stains for bacteria (Gram stain and Ziehl–Neelsen stain) and fungi (periodic acid‐Schiff stain) were all negative. On immunohistochemistry, the neoplastic cells showed strong cytoplasmic positivity for Iba‐1 and CD204, but were negative for CD3 and CD20. Transmission electron microscopy failed to detect Birbeck's granules in the cytoplasm of the neoplastic histiocytes. The chinchilla received chemotherapy with lomustine but died spontaneously on day 62 despite treatment. Autopsy with histopathologic examination revealed disseminated histiocytic sarcoma involving the bone marrow, bronchial lymph nodes, nasal cavity, lung, heart, stomach, pancreas, pancreatic lymph nodes, liver, spleen, and kidney. To the best of our knowledge, this is the first report of disseminated histiocytic sarcoma in chinchillas.

Clinical, histopathological, and immunohistochemical studies of histiocytic sarcoma in four-toed hedgehogs (Atelerix albiventris): A retrospective study

Histiocytic sarcoma was investigated histopathologically and immunohistochemically in 17 four-toed hedgehogs (Atelerix albiventris), along with a review of their clinical data. Cases were histopathologically classified into two types: round-polygonal cell type (6 cases) and spindle cell type (11 cases). Round-polygonal cell type was found in visceral organs such as the spleen, lymph nodes, and more, and most cases of this type were consistent with disseminated histiocytic sarcoma. On the other hand, spindle cell type occurred mainly in skin, and almost all cases were consistent with localized histiocytic sarcoma. The prognosis of patients with round-polygonal cell type appeared worse than that of spindle cell type. Immunohistochemically, neoplastic cells of spindle cell type showed stronger reactivity against human leukocyte antigen-DR than round-polygonal cell type. Neoplastic cells of all cases showed strong reactivity against ionized calcium-binding adapter molecule-1 (Iba-1) and various reactivities against cluster of differentiation (CD) 204. Regardless of morphological classification, most tumor cells were negative for CD163, suggesting that this marker is less effective for the diagnosis of histiocytic sarcoma. The results of this study suggest that Iba-1 is the most effective marker for histiocytic sarcoma.

Giant Cell Sarcomas in Domestic Rabbits (Oryctolagus cuniculus)

Multinucleated giant cells (MGCs) are a prominent histological feature of various mesenchymal neoplasms and are often considered a criterion of malignancy. Mesenchymal neoplasms with MGCs for which the cell lineage is unclear generally are referred to as giant cell sarcomas. Here we characterize the gross, histologic, and immunohistochemical features of 90 giant cell sarcomas in domestic pet rabbits. Based on the anatomic location and histologic and immunohistochemical findings, 18 cases were classified as histiocytic sarcomas (HS) and 72 cases as anaplastic sarcomas (AS). At postmortem examination, HS was either localized HS (n = 7) always affecting the lungs, or disseminated HS (n = 10) that affected the lungs (n = 10), liver (n = 6), kidneys (n = 4), pleura (n = 2), mediastinum (n = 2), heart (n = 4), skeletal muscle (n = 1), adipose tissue (n = 1), and lymph node (n = 1). Additionally, one cecal biopsy was consistent with HS. Microscopically, HS were characterized by sheets of neoplastic polygonal to round cells that contained single to several, often greatly enlarged nuclei as well as abundant cytoplasm. HS were always positive for CD204 and always negative for SMA and desmin. In contrast, AS arose most commonly from the skin or subcutis (n = 62) and rarely the skeletal muscle (n = 8) or abdominal organs (n = 2). In 29% of extra-abdominal AS, the tumor deeply invaded into surrounding connective tissue, skeletal muscle, tendons, and bone causing pathological fractures. Five of 9 postmortem cases metastasized to various organs often including the lungs. Microscopically, AS were characterized by sheets of spindle or pleomorphic cells admixed with variable numbers of MGCs. Immunohistochemically, AS were always negative for CD204 and often (71%) positive for SMA and/or desmin.

Disseminated histiocytic sarcoma with hemophagocytosis in a rabbit

A 7-year-old female domestic rabbit suffered from labored respiration, poor appetite, mild anemia and thrombocytopenia. Radioscopic examination revealed masses in multiple locations including the intrapleural cavity and spleen. Forty-three days after the first visit to a private veterinary clinic, the rabbit died of severe respiratory distress. Microscopically, all of the masses were composed of round to polygonal neoplastic cells with distinct cell borders that were arranged in a sheet pattern. Multinucleated giant neoplastic cells were often observed. Some neoplastic cells had phagocytozed one or more erythrocytes. Immunohistochemical staining revealed that the neoplastic cells expressed vimentin, CD204, Iba-1 and lysozyme, but not CD163. Based on the morphological and immunohistochemical findings, this case was diagnosed as disseminated histiocytic sarcoma with hemophagocytosis.

Cutaneous Histiocytic Sarcoma with Regional Lymph Node Metastasis in a Netherland Dwarf Rabbit (Oryctolagus cuniculus)

A 10-year-old male Netherland dwarf rabbit (Oryctolagus cuniculus) was presented with a red nodular mass (1 cm in diameter) with ulceration and hair loss in the skin of the left upper lip. Cytological examination revealed atypical round cells. The mass was excised surgically. Histologically, the mass was composed of large round to polyhedral neoplastic cells with marked cytological atypia. The neoplastic cells were often binucleated or multinucleated. Immunohistochemically, the neoplastic cells were intensely positive for Iba1 and vimentin, but fewer neoplastic cells expressed E-cadherin. Nuclear immunoreactivity for Ki67 was detected in approximately 41% of the neoplastic cells. Metastasis to the left cervical lymph nodes was detected 6 months after the surgical excision. Based on clinical, histopathological and immunohistochemical findings, the present case was diagnosed as cutaneous histiocytic sarcoma. To the authors' knowledge cutaneous histiocytic disease has not been reported previously in lagomorphs.

Histological and immunohistochemical features of histiocytic sarcoma in four domestic ferrets (Mustela putorius furo)

Four cases of histiocytic sarcoma in domestic ferrets (Mustela putorius furo) are described in the present study. Tumor samples obtained from the abdominal viscera, including the spleen, were submitted for histologic examination. Microscopically, poorly demarcated masses contained numerous round- to pleomorphic-shaped cells with coarsely vacuolated and eosinophilic cytoplasm. Bizarre, binucleated tumor cells and multinucleated giant tumor cells with low phagocytic activity were commonly observed. Immunohistochemically, tumor cells in all of the cases were positive for vimentin, human leukocyte antigen-DR, ionized calcium-binding adapter molecule-1, and lysozyme, but some of them lacked cluster of differentiation (CD)163 or CD208 expression. The survival time after surgical resection was 9 days to 5 months. Histiocytic sarcoma in the ferret is a rare, but highly aggressive, tumor commonly found in the spleen.