Two hundred three cases of equine lymphoma classified according to the World Health Organization (WHO) classification criteria.
Authors: Durham A C, Pillitteri C A, San Myint M, Valli V E
Journal: Veterinary pathology
Summary
# Editorial Summary Lymphoma represents the most prevalent malignancy in horses, yet our understanding of its clinical diversity and biological subtypes has remained fragmented across isolated case reports and small institutional series. Durham and colleagues examined 203 equine lymphoma cases from eight veterinary institutions, performing histopathological review and immunophenotyping on 187 cases using WHO classification criteria—the first large-scale standardised characterisation of equine lymphoid malignancies. The cohort spanned ages 2 months to 31 years (mean 10.7 years) across 24 breeds, with Quarter Horses, Thoroughbreds, and Standardbreds most frequently affected; notably, multicentric disease predominated (n=83), followed by cutaneous (n=38) and gastrointestinal presentations (n=24), whilst 14 distinct lymphoma subtypes were identified, with T-cell-rich large B-cell lymphomas being most common (n=87), followed by peripheral T-cell lymphomas (n=45) and diffuse large B-cell lymphomas (n=26). These findings provide equine practitioners with a robust morphological and immunological framework for lymphoma diagnosis and subtype classification, enabling more accurate prognostication and facilitating comparison of treatment responses and outcomes across cases—essential groundwork for advancing evidence-based protocols in equine oncology and identifying breed predispositions that may warrant genetic investigation.
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Practical Takeaways
- •Lymphoma is common in horses and presents in diverse forms; standardized WHO classification helps guide prognosis and treatment discussions with owners
- •Multicentric, cutaneous, and gastrointestinal presentations are most frequent—clinicians should maintain suspicion for lymphoma in middle-aged to older horses with these signs
- •Immunophenotyping is essential for accurate subtype classification, which may influence treatment planning and prognostic counseling
Key Findings
- •203 equine lymphoma cases were classified using WHO criteria, identifying 14 distinct lymphoma subtypes
- •T-cell-rich large B-cell lymphomas were the most common subtype (n=87), followed by peripheral T-cell lymphomas (n=45) and diffuse large B-cell lymphomas (n=26)
- •Multicentric presentation was most common (n=83), with cutaneous (n=38) and gastrointestinal (n=24) sites also frequently affected
- •Mean age at diagnosis was 10.7 years (range 2 months to 31 years); Quarterhorses, Thoroughbreds, and Standardbreds were most commonly affected