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Cutaneous neoplastic lesions of equids in the central United States and Canada: 3,351 biopsy specimens from 3,272 equids (2000–2010)

Paula A. Schaffer DVM1, Bruce Wobeser DVM, MVetSci, PhD, DACVP2, Laura E. R. Martin BS3, Michelle M. Dennis DVM, PhD, DACVP4,5, and Colleen G. Duncan DVM, MSc, PhD, DACVP, DACVPM6
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  • 1 Department of Microbiology, Immunology, and Pathology and the Veterinary Diagnostic Lab, College of Veterinary Medicine and Biological Sciences, Colorado State University, Fort Collins, CO 80523.
  • | 2 Department of Veterinary Pathology, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, SK S7N 5B4, Canada.
  • | 3 Department of Microbiology, Immunology, and Pathology and the Veterinary Diagnostic Lab, College of Veterinary Medicine and Biological Sciences, Colorado State University, Fort Collins, CO 80523.
  • | 4 Department of Microbiology, Immunology, and Pathology and the Veterinary Diagnostic Lab, College of Veterinary Medicine and Biological Sciences, Colorado State University, Fort Collins, CO 80523.
  • | 5 QML Vetnostics, 11 Riverview Pl, Brisbane, QLD 4172, Australia.
  • | 6 Department of Microbiology, Immunology, and Pathology and the Veterinary Diagnostic Lab, College of Veterinary Medicine and Biological Sciences, Colorado State University, Fort Collins, CO 80523.

Abstract

Objective—To identify epidemiological trends in cutaneous neoplasms affecting equids in central North America and compare them with previously reported trends.

Design—Retrospective case series.

Sample—3,351 cutaneous biopsy specimens from 3,272 equids with a neoplastic diagnosis.

Procedures—Diagnostic reports from 2 diagnostic laboratories (Colorado State University and Prairie Diagnostic Services Inc) were reviewed for frequency of specific lesions and epidemiological trends. Variables included in analyses (if known) were age, sex, breed, geographic location, date of diagnosis, location of neoplasm on the body, and presence or absence of ulceration.

Results—Sarcoid, squamous cell carcinoma (SCC), and melanoma were the 3 most common tumors diagnosed. Tumors associated with UV radiation (SCC, SCC in situ, hemangioma, hemangiosarcoma) were 2.3 (95% confidence interval [CI], 1.8 to 3.0) times as common in biopsy specimens received by Colorado State University than in specimens received by Prairie Diagnostic Services Inc. Appaloosa horses and American Paint horses, respectively, were 7.2 (95% CI, 5.6 to 9.2) and 4.4 (95% CI, 3.6 to 5.4) times as likely as other breeds to have tumors associated with UV radiation. Thoroughbreds were predisposed to cutaneous lymphoma, whereas Arabians were more likely to have melanomas. Draft and pony breeds were 3.1 (95% CI, 1.9 to 5.1) times as likely as other breeds to have benign soft tissue tumors. Morgans and pony breeds more commonly had basal cell tumors. Tumors in the perianal region were significantly more likely to be SCC or melanoma while tumors on the limbs were more likely to be giant cell tumor of soft parts.

Conclusions and Clinical Relevance—Signalment, anatomic location of the mass, and geographic location of the horse can be used to help equine practitioners formulate differential diagnoses for cutaneous masses. Further research is necessary to identify the biological basis for the development of many equine cutaneous neoplasms.

Contributor Notes

Supported by the Colorado State University Diagnostic Laboratory with funds provided by Mary Lou Lane.

The authors thank Jay Kammerzell for assistance with data acquisition and organization.

Address correspondence to Dr. Duncan (Colleen.Duncan@colostate.edu).