Morphological Distinction of Histiocytic Sarcoma from Other Tumor Types in Bernese Mountain Dogs and Flatcoated Retrievers

Abstract

Background/aim: Histiocytic sarcoma (HS) represents a group of malignant canine tumors to which Bernese Mountain Dogs (BMD) and Flatcoated Retrievers (FCR) are predisposed. The differential diagnosis for HS is broad, encompassing round cell tumors, sarcomas and other histiocytic diseases. The aim of this study was to establish morphological and immunohistochemical criteria for routine use on formalin-fixed, paraffin-embedded samples and cytological smears for the recognition and differentiation of canine HS and its subtypes.

Materials and methods: Retrospectively, tumor sections were reviewed from 449 BMD and 380 FCR with confirmed or suspected HS, other histiocytic conditions, or a disease of the differential diagnosis of HS.

Results: In a large proportion of cases, 47.5% for histology and for 46.3% cytology, the initial diagnosis was changed after the revision process. A large variation in morphological features of HS was observed in this study, making the existence of several subtypes in dogs also very likely. Furthermore, the different percentage of morphological features between BMD and FCR indicates the different mixture of cell type origins resulting possibly from genetic or environmental differences at the onset of HS in those breeds.

Conclusion: This study stresses the value of a strictly applied and standardized scoring system for microscopic evaluation of tumor sections and smears, and the implementation of review and revision of pathological diagnoses.

Keywords: Bernese Mountain Dog; Canine; Flatcoated Retriever; comparative pathology; cytology; histiocytic sarcoma; histo(patho)logy; immunohistochemistry.