Diagnosis and Classification of Primary Nodal Lymphomas in Dogs: A Consensus of the Oncology‐Pathology Working Group

: One of the primary objectives of the Oncology Pathology Working Group (OPWG) is for oncologists and pathologists to collaboratively generate consensus documents to standardise aspects of and provide guidelines for oncologic pathology in veterinary species. Consensus is established through critical review of the peer-reviewed literature relevant to a subgroup's particular focus. In this article, the authors provide a critical review of the current literature regarding methods for the diagnosis and classification of primary nodal lymphomas of dogs, including histopathology, cytopathology, immunophenotyping and assessment of molecular clonality. Knowledge gaps in the current literature and recommendations for future study are also reported. Major conclusions of this consensus include: (1) Histopathology with immunohistochemistry is required for complete diagnosis and classification of nodal lymphomas; (2) Immunohistochemistry and flow cytometry are the most reliable methods of immunophenotyping lymphomas, though neither is clearly superior to the other; (3) Molecular clonality testing should not be used in favour of immunophenotyping assays for classifying lymphomas; and (4) The use of emerging molecular tests for diagnosing lymphomas in the absence of histopathologic, cytopathologic, or immunophenotypic disease characterisation should be restricted to investigational settings until their diagnostic validity and the clinical benefit they confer to patients are more thoroughly characterised. This document represents the opinions of the OPWG and the authors; it does not constitute a formal endorsement by the American College of Veterinary Pathologists or the Veterinary Cancer Society.