Mixed histiocytic sarcoma in a Bernese Mountain Dog.

Area of Science:

• Veterinary Pathology
• Canine Oncology
• Comparative Oncology

Background:

• A Bernese Mountain Dog presented with lameness and poor response to immunosuppression, initially suspected of Evans syndrome.
• Diagnostic review suggested hemophagocytic histiocytic sarcoma (HHS) was more likely than Evans syndrome.
• Atypical histiocytic cells with siderophagia were observed in blood smears.

Purpose of the Study:

• To investigate the diagnosis of a canine patient with atypical circulating neoplastic cells.
• To characterize the histiocytic sarcoma (HS) subtype and its origin.
• To explore the diagnostic challenges associated with rare neoplastic cell types.

Main Methods:

• Review of clinical findings and laboratory data.
• Blood smear evaluation for atypical cells.
• Autopsy and histopathology for definitive diagnosis.
• Immunocytochemical characterization of cultured cells.
• Whole-exome sequencing for genetic analysis.

Main Results:

• The dog was diagnosed with a mixed form of histiocytic sarcoma (HS), involving dendritic-cell origin HS in the lung and HHS in multiple organs.
• Cultured blood cells were identified as dendritic HS origin, not HHS.
• Whole-exome sequencing confirmed genetic similarity between lung and blood cell lines.
• The case presented challenges in classifying atypical circulating neoplastic cells.

Conclusions:

• Mixed histiocytic sarcoma is a rare entity in dogs.
• Accurate classification of circulating neoplastic cells can be challenging.
• This case underscores the importance of comprehensive diagnostics for rare canine cancers.