What is the prognosis and staging approach for histiocytic sarcoma in Bernese Mountain Dogs?

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Prognosis for histiocytic sarcoma (HS) in Bernese Mountain Dogs (BMDs) is poor regardless of treatment form, with a median survival of 170 days across all dogs with HS. Subgroup analysis identifies disseminated HS and palliative treatment as statistically significant negative prognostic factors for survival. 3 Staging is based on extent of disease at diagnosis, with HS classified as localized (confined to a single organ or local lymph nodes) or disseminated (widespread multi-organ involvement). Disseminated HS is recorded significantly more frequently in BMDs (60.8%) than in Flat-Coated Retrievers (39.4%), making disseminated disease the predominant presentation in this breed. 8 Common primary sites include the spleen, lymph nodes, lungs, bone marrow, CNS, skin, subcutis, and periarticular tissues; secondary dissemination frequently involves the liver, lungs, and hilar lymph nodes. 6 If an internal organ is affected, disseminated disease is often already present at the time of diagnosis. 4 The staging workup should include thoracic imaging, abdominal imaging, and evaluation of bone marrow, given the typical dissemination pattern. Computed tomography detects lesions in pulmonary tissue, thoracic lymph nodes, spleen, kidney, and bone with accuracy comparable to autopsy, though hepatic nodules are difficult to detect with standard CT protocols — CT identified hepatic lesions in 2 of 7 cases confirmed at autopsy. 13 Cytology and histopathology with immunophenotyping are required to confirm histiocytic lineage, as HS can resemble other round cell tumors, anaplastic carcinomas, and sarcomas on morphology alone. 6 CD18 positivity and pancytokeratin negativity confirm histiocytic origin. 1012 Hematologic staging findings in BMDs include leukocytosis and thrombocytopenia, which occur significantly more often in BMDs than in Flat-Coated Retrievers even after correcting for HS type. Hypercalcemia was identified in 15 BMDs with HS and in none of the Flat-Coated Retrievers evalu