Rhabdomyosarcoma in 8 horses.
Authors: Castleman W L, Toplon D E, Clark C K, Heskett T W, Farina L L, Lynch T M, Bryant U K, Del Piero F, Murphy B, Edwards J F
Journal: Veterinary pathology
Summary
Rhabdomyosarcoma remains an uncommon but significant malignancy in horses, with presentation and prognosis varying considerably depending on anatomical location and tumour size. This multi-institutional pathological review examined eight cases—including four oral/head lesions, two abdominal wall masses, one shoulder tumour, and one cardiac mass—and synthesised findings with nine previously published equine cases to establish patterns in disease behaviour and treatment response. Smaller tumours (under 10 cm) managed surgically or with radiation therapy showed no recurrence, whilst larger lesions (over 10 cm) in weight-bearing or critical locations proved inoperable and resulted in euthanasia; across all 17 cases analysed, limb muscles and tongue were the predominant sites. Most tumours were embryonal type, though pleomorphic variants occurred, and whilst metastatic disease had been documented in prior case reports, none developed in this cohort. For practitioners, these findings suggest that early detection and intervention for oral and accessible soft tissue lesions offer genuine curative potential, but location, size assessment, and realistic appraisal of surgical feasibility remain paramount to determining whether treatment or palliative management is appropriate.
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Practical Takeaways
- •Smaller rhabdomyosarcomas (< 10 cm) in horses have a better prognosis with surgical or radiation treatment and may be managed without recurrence
- •Larger tumors (> 10 cm) in weight-bearing or critical locations are likely inoperable; early detection and intervention is crucial
- •Maintain high clinical suspicion for rhabdomyosarcoma in horses presenting with oral/lingual masses or muscle neoplasias, as embryonal type predominates
Key Findings
- •Rhabdomyosarcomas < 10 cm diameter treated surgically or by radiation showed no recurrence in 4 cases
- •Rhabdomyosarcomas > 10 cm diameter in abdominal wall and shoulder were considered inoperable and led to euthanasia
- •Embryonal rhabdomyosarcoma was the predominant histological type (7/8 cases)
- •Combined review of 17 cases identified limb muscles (5/17) and tongue (4/17) as most common sites, with metastasis reported in 4 previously published cases but none in this series