Introduction

• Lymphoma and lymphosarcoma are used interchangeably to describe neoplasia arising from the lymphoid system (lymph nodes, thymus, spleen, mucosal-conjunctival and skin-associated lymphoid tissue).
• Most common hematopoietic neoplasm in horses
• 1.3-2.8% of all equine tumors; less common than sarcoid Sarcoid, squamous cell carcinoma Skin: neoplasia - squamous cell carcinoma, melanoma Skin: neoplasia - melanoma, granulosa cell tumor Ovary: neoplasia - granulosa theca cell. A recent UK database survey of equine tumors identified a prevalence of lymphoma of 14% from 964 neoplastic equine histology submissions to a diagnostic pathology laboratory.
• Tumors are frequently multicentric, involving lymph nodes and thoracic and abdominal organs Gastrointestinal: neoplasia.
• Cutaneous lymphosarcomas are more benign in nature and can be treated successfully via wide local excision in the early stages.
• Lymphocytes are widespread and neoplasia may occur in most tissues.
• Leukemia is rare, but if identified it indicates bone marrow infiltration.
• Wide age range, average around 6-10 years (Note: it is not the preserve of older horses).
• No sex or breed predilection.
• Often insidious onset but can present relatively acutely following change/deterioration in condition, giving a more rapid clinical course (except cutaneous form).
• Diagnosis can be challenging, as often present with non-specific clinical signs depending on the primary organs involved. Definitive diagnosis relies on identification of malignant lymphoid cells in blood or bone marrow, pleural or peritoneal fluid, tissue sections or aspirates.
• See also:
  • Gastrointestinal lymphosarcoma Gastrointestinal: neoplasia.
  • Ovarian lymphosarcoma Ovary: neoplasia - overview.
  • Cutaneous lymphosarcoma Skin: neoplasia - lymphosarcoma.
  • Thoracic lymphosarcoma Respiratory: neoplasia.

Clinical signs

• Diverse clinical signs due to range of pathology, but defined pathological forms do have some distinct clinical signs (with some overlap).
• Signs reflect space-occupying tumors and the effects of products of neoplastic cells.
• Non-specific signs:
  • Weight loss, anorexia, depression, ventral edema (can be due to reduced protein loss and oncotic pressure or impaired lymphatic drainage due to tumor infiltration of lymph nodes).
  • Diarrhea.
  • Colic.
  • Neutrophilia, hyperglobulinemia, hyperfibrinogenemia.
  • Cytopenia affecting one or more hematopoietic cell lines, anemia most common (may be due to blood loss Anemia: blood loss, anemia of chronic disease Anemia: chronic disease, immune-mediated hemolytic anemia Anemia: auto-immune hemolytic (AIHA), infiltration of bone marrow leading to neutropenia and thrombocytopenia).
  • Biochemical changes reflect infiltration of organs, eg hypoalbuminemia Blood: biochemistry - albumin, increased ALP Blood: biochemistry - alkaline phosphatase (SAP, ALP), hypercalcemia.
• Paraneoplastic syndrome, eg hypercalcemia Hypercalcemia, pruritus, alopecia Hair: alopecia areata, mucosal ulceration, immune-mediated hemolytic anemia Anemia: auto-immune hemolytic (AIHA), thrombocytopenia Thrombocytopenia: overview, hypertrophic osteopathy (HO; Marie’s Disease).

Treatment

• Surgical excision of single masses, chemotherapy. Anti-neoplastic chemotherapy is very expensive and case selection is vital.
• Prednisolone Prednisolone can be a useful palliative treatment.
• Horses with lymphoma, particularly multicentric form, are often euthanized within weeks to months after diagnosis due to poor condition. 

Diagnostic investigation

Biochemistry

• D-xylose or glucose absorption test Gastrointestinal: intestinal function tests.

Ultrasonography

• Abdominal Ultrasonography: abdomen and thoracic ultrasound Ultrasonography: thorax.

Radiography

• Thoracic radiography Thorax: radiography.

Laboratory testing

• Analysis of peritoneal/pleural effusions.
• Histopathology of affected organs/masses/lymph nodes.
• Duodenal and rectal biopsies may prove useful if widespread intestinal disease is present.
• Peritoneal fluid may contain exfoliated lymphoma cells in up to 50% of cases of intra-abdominal lymphoma cases.

Surgical investigation

• Thoracoscopy Thorax: thoracoscopy.
• Laparoscopy Abdomen: laparoscopy.
• Laparotomy Abdomen: laparotomy. 

Postmortem

Gross

• Depends on location and extent of tumor infiltration (see classifications below).

Classifications

Treatment

Outcomes

Further Reading

Publications

Refereed Papers

• Recent references from PubMed and VetMedResource.
• Janvier V, Evrard L, Cerri S, Gougnard A & Busoni V (2016) Ultrasonographic findings in 13 horses with lymphoma. Vet Radiol Ultrasound 57 (1), 65-74 PubMed.
• Knowles E J, Tremaine W H, Pearson G R & Mair T S (2015) A database survey of equine tumours in the United Kingdom. Equine Vet J  48 (3), 280-284 PubMed.
• Larsdotter S, Nostell K & von Ender H (2015) Serum thymidine kinase activity in clinically healthy and disease horses: a potential marker for lymphoma. The Vet J  205 (2), 313-316 PubMed.
• Moser D K et al (2014) Hindlimb lameness caused by systemic lymphosarcoma in a Warmblood mare. Equine Vet Educ 26 (8), 416-419 WileyBlackwell.
• Johns I C et al (2014) Diagnosis, treatment and outcome of spinal lymphoma in a pony. Equine Vet Educ 26 (6), 303-305 VetMedResource.
• Davis E G and Rush B R (2013) Diagnostic challenges: equine thoracic neoplasia. Equine Vet Educ 25 (2), 96-107 VetMedResource.
• Rendle D (2013) Poor performance due to disseminated lymphoma in an Arab gelding. UK Vet 18, 4-7 WileyBlackwell.
• Greet T R C, Boys Smith S J, Foote A K & Steven W N (2011) Mandibular lymphoma in a three-year-old thoroughbred filly. Vet Rec 168 (3), 80 PubMed.
• Barrelet A, Foote A & Littlewood J D (2010) Common equine skin tumours. UK Vet 15 (6), 9-17 WileyBlackwell.
• Roberts M C (2008) Equine lymphoma: What are the prospects for cellular differentiation, early diagnosis and intervention strategies? Equine Vet Educ 20 (9), 464-466 VetMedResource.
• Scase T J (2008) Classification of equine lymphoma. Equine Vet Educ 20 (9), 467-468 VetMedResource.
• Sheats M K, van Wetter A J N J, Snyder L A & Jones S L (2008) Disseminated large granular lymphoma in a horse. Equine Vet Educ 20 (9), 459-463 VetMedResource.
• Meyer J, DeLay J and Bienjle D (2006) Clinical, laboratory and histopathological features on equine lymphoma. Vet Pathol 43 (6), 914-924 PubMed.
• Henson F M D, Dixon K & Dobson J M (2004) Treatment of 4 cases of equine lymphoma with megavoltage radiation. Equine Vet Educ 16 (6), 312-314 VetMedResource.
• Zimmerman B, Jones S & Rotstein D S (2004) Large granular lymphoma in a mule. Vet Rec 155 (15), 463-465 PubMed.
• De Clercq D, van Loon G, Lefere L & Deprez P (2004) Ultrasound-guided biopsy as a diagnostic aid in three horses with cranial mediastinal lymphosarcoma. Vet Rec 154 (23), 722-726 PubMed.
• Henson K L et al (2000) Immunohistochemical characterization of estrogen and progesterone receptors in lymphoma of horses. Vet Clin Pathol 29 (2), 40-46 PubMed.
• Kelley L C & Mahaffey E A (1998) Equine malignant lymphomas - morphological and immunohistochemical classification. Vet Pathol 35 (4), 241-252 PubMed.
• Lester G D, Allemen A R, Rakin R E et al (1993) Pancytopenia secondary to lymphoid leukaemia in three horses. J Vet Intern Med 7, 360-363 PubMed.
• Dascanio J J, Zhang C H, Anczack D F et al (1992) Differentiation of chronic lymphocytic leukaemia in the horse. J Vet Intern Med 6, 225-229 PubMed.
• Furr M O, Crisman M V et al (1992) Immunodeficiency associated with lymphosarcoma in a horse. JAVMA 201 (2), 307-309 PubMed.
• Mair T S & Hillyer M H (1991) Clinical features of lymphosarcoma in the horse - 77 cases. Equine Vet Educ 4, 108-113 WileyBlackwell.
• Bernard W V, Sweeney C R & Morris F (1988) Primary lymphocytic leukaemia in a horse. Equine Pract 10 (10), 24-30.
• Grindem C B, Roberts M C et al (1988) Large granular lymphocyte tumour in a horse. Vet Pathol 26 (1), 86-88 PubMed.
• Van den Hoven R & Franken P (1983) Clinical aspects of lymphosarcoma in the horse. Equine Vet J 5 (1), 49-53 PubMed.
• Neufield J L (1973) Lymphosarcoma in the horse: A review. Can Vet J 14 (6), 129-135 PubMed.