Histologic, Phenotypic, and Molecular Characterization of Feline Hodgkin-Like Lymphoma With Classical Reed-Sternberg Cells.

Hodgkin-like lymphoma (HLL) is a rare neoplasm in cats that shares characteristics with the human disease. The hallmark of HLL is the presence of Reed-Sternberg (RS) cells expressing CD30 and CD20. This study aimed to elucidate the clinicopathologic features, immunophenotype and clonality patterns of feline HLL. A comprehensive retrospective review of clinicopathologic and molecular data of nodal lymphomas over a 6-year period was conducted in MyLav laboratory. Twenty-four cases were identified. All cats presented with submandibular or retropharyngeal lymphadenopathy. Histopathologic examination revealed a multifocal to diffuse proliferation of medium-to-large lymphoid cells with low mitotic activity, interspersed RS cells, and a heterogeneous inflammatory infiltrate comprising T-cells, plasma cells and neutrophils. In addition, extensive necrosis was a consistent finding. Immunohistochemistry showed a variable membranous CD20 and nuclear PAX5 expression in neoplastic cells, while RS cells displayed only mild to moderate CD20 positivity and were negative to PAX5. In 21/24 cases (87.5%), RS cells were diffusely CD30-positive. PARR analysis demonstrated clonal B-cell expansion in 60% of cases, with the remaining 40% exhibiting polyclonality. For the 10 cats with available follow-up, the prognosis was generally favourable, with only two cats succumbing to progressive disease. In conclusion, diagnosing feline HLL is challenging. The expression of CD30 and CD20 by RS cells should be considered a hallmark of the disease, but only after excluding differential diagnoses such as anaplastic B-cell lymphoma and granulomatous lymphadenopathy.