Spotlight on equine hemangiosarcoma

Josepha DeLay, Andrew Brooks, Murray Hazlett, Amanda Mansz, Maria Spinato

Animal Health Laboratory, University of Guelph, Guelph, ON

AHL Newsletter 2021;25(2):25.

Hemangiosarcomas are uncommon neoplasms in horses.  These malignant tumors are composed of neoplastic endothelial cells often lining variably-sized vascular spaces (Fig. 1).  As a result, hemorrhage is a common clinical and histologic feature.  Equine hemangiosarcomas may present as solitary neoplasms at a variety of anatomic sites, or as disseminated tumors involving multiple organs.  In horses, hemangiosarcomas have been described in skin, ocular and periocular sites (limbus, conjunctiva, third eyelid, uvea), kidney, heart, brain, lung, and other internal organs. 

Between May 2007 and May 2021, 9 cases of equine hemangiosarcoma were recorded in the Animal Health Laboratory database, including 4 postmortem cases and 5 biopsies.  Solitary tumors occurred in 6 horses and were cutaneous (2), ocular (limbus or third eyelid - 2), or involved soft tissue (neck -1 or unknown site-1).  Disseminated tumors in 3 horses involved 2 or more internal organs, including skeletal muscle and kidney (1), liver and spleen (1), and kidney, ovary, brain, lung, epaxial muscle, and vertebrae (1). 

The age range for all horses with hemangiosarcoma was 3 months to 22 years (mean 10.6 years, median 11.5 years).  Age was unknown for 1 horse in the series.  Horses with solitary tumors tended to be younger (age range 3 months to 15 years, mean 7.25 years) compared to those with disseminated neoplasia (age range 13-22 years, mean 16.2 years).  However the total number of animals in this series is too low to draw significant conclusions about age distribution of tumor subtypes in horses.  Other studies have described a subset of hemangiosarcomas in young horses <3 years of age, including congenital tumors, and with primarily skin and limb involvement.

Clinical signs in horses with hemangiosarcoma reflect the location of the neoplasm, such as abdominal pain and weight loss for tumors in kidney or other abdominal organs.  Hemorrhage into body cavities may occur in horses with tumors involving internal organs and may manifest as anemia.  The clinical differential diagnoses for the 2 cutaneous tumors in this series were sarcoid and exuberant granulation tissue (proud flesh), both of which are more common equine cutaneous lesions; histopathology of lesion biopsies is required for differentiation.  Exposure to sunlight is suggested in the pathogenesis of ocular hemangiosarcoma and in cutaneous tumors in non-pigmented skin.

For solitary tumors, radical surgical excision is the treatment of choice, with the addition of ancillary therapy in some cases.  Some reports describe a favorable prognosis for cutaneous and ocular hemangiosarcomas that are completely excised.  However, extensive studies are not available for prognosis of localized equine hemangiosarcomas due to the low incidence of the neoplasm in this species.   Prognosis is poor for disseminated hemangiosarcomas in horses and other species.

Thank you to former Ontario Veterinary College Department of Pathobiology graduate students for their diagnostic contributions to these cases: Dr. Hibret Adissu, Dr. Fernanda Castillo, and Dr. Courtney Schott.  AHL

Figure 1. Cutaneous hemangiosarcoma in a 2-year-old horse.  Plump neoplastic spindle (endothelial) cells forming multiple small, haphazardly arranged blood-filled spaces. H&E stain.

References

1. Beaumier A, et al. Primary cardiac hemangiosarcoma in a horse: Echocardiographic and necropsy findings.  J Vet Cardiol 2020;32: 66-72. 

2. Hughes K, et al. Equine renal hemangiosarcoma: Clinical presentation, pathologic features, and pSTAT3 expression.  J Vet Diagn Invest 2018;30(2):268-274.

3. Johns I, et al. Hemangiosarcoma in 11 young horses.  J Vet Intern Med 2005;19(4):564-570.

4. Scherrer NM, et al. Ocular and periocular hemangiosarcoma in six horses.  Vet Ophthalmol 2018;21(4):432-437.

5. Southwood LL, et al. Disseminated hemangiosarcoma in the horse: 35 cases.  J Vet Intern Med 2000;14(1):105-1099.