1.0 Introduction
Lymphoma in the horse is uncommon but is the most common hematopoietic
neoplasm in equids accounting for 1-14% of all equine neoplasms with a
prevalence of 0.02 – 0.5% in the equine population (Savage 1998;
Schneider 2003; Knowles et al. 2016). There is no sex, breed or
age predilections and lymphoma has been reported in all stages of life
from fetal to geriatric (Haley and Spraker 1983; Meyer et al. 2006). Lymphoma can be expressed in various forms including
multicentric, alimentary, cutaneous, mediastinal or solitary extranodual
tumors and the immunophenotype is important for classification and
treatment planning (Sheard and McGovern 2021).
A retrospective study of 203 equine lymphoma cases utilized the World
Health Organization (WHO) Classification System based on
immunophenotyping. This retrospective study identified T-cell-rich,
large B-cell (TCRLBCL) as the most common immunophenoytype representing
43% of cases and diffuse large B-cell (DLBC) the 3rdmost common accounting for 26 or 12.5% of the 187 reported cases with
immunohistochemistry (Durham et al. 2013). The multicentric form
of the disease is the most common and is often found in younger horses
aged 4 to 10 years old, whereas the alimentary form is more commonly
found in horses greater than 16 years old (Schneider 2003; Meyeret al. 2006; Taintor and Schleis 2011; Durham et al. 2013). Organs most typically affected with the multicentric form include
the lymphatic system, spleen, liver, intestine, kidney, lung and
occasionally bone marrow (Sheard and McGovern 2021). Clinical signs are
insidious and non-specific, varying with the affected organs but most
often include depression, edema of distal limbs or ventral abdominal
wall, weight loss, pyrexia and cachexia (Meyer et al. 2006; Muñozet al. 2009).