Histiocytic Sarcoma

Histiocytic sarcoma (HS) is an aggressive neoplasm primarily arising from dendritic cells, with a strong breed predisposition in Bernese Mountain Dogs, Flat-coated Retrievers, and Miniature Schnauzers. The disease typically affects middle-aged to older dogs and can manifest localized, multifocal, or disseminated lesions, commonly affecting organs such as the lung, spleen, liver, and lymph nodes. Periarticular HS (PAHS) is the most common tumor of the canine joint, but its histologic appearance overlaps with synovial cell sarcoma, necessitating immunohistochemistry for definitive diagnosis. Genetic predisposition and preexisting joint disease may contribute to the development of HS, with studies suggesting a heritable risk factor, particularly in Miniature Schnauzers with primary pulmonary HS. Clinical presentation varies widely, with nonspecific signs such as lethargy, anorexia, and weight loss, or more specific symptoms like lameness (in PAHS) or anemia-related symptoms (in hemophagocytic HS). Diagnostic evaluation typically involves cytology, histopathology, and immunohistochemistry, with standard diagnostic workups including physical examination, complete blood count, and imaging studies. Treatment options include surgery, chemotherapy (primarily CCNU for non-hemophagocytic HS), targeted therapy (e.g., trametinib and lapatinib for ERK and Akt pathway inhibition), and steroids.