Rhabdomyosarcoma in a Rabbit

Area of Science:

• Veterinary Pathology
• Oncology
• Rabbit Medicine

Background:

• Rhabdomyosarcoma is a rare malignant tumor of mesenchymal origin, typically affecting soft tissues.
• Pleomorphic rhabdomyosarcoma is a subtype characterized by significant cellular and nuclear variation.
• Geriatric rabbits can be susceptible to various neoplastic conditions, impacting their quality of life.

Observation:

• A geriatric Holland Lop rabbit presented with acute lameness due to a pathologic fracture of the right distal femur.
• Radiographic staging revealed no overt metastasis at the time of initial diagnosis.
• The tumor was identified as a pleomorphic rhabdomyosarcoma.

Findings:

• Immunohistochemical analysis confirmed neoplastic cells positive for desmin and MyoD1, consistent with rhabdomyosarcoma.
• The tumor cells were negative for cytokeratin AE1/AE3, CD204, IBA-1, and SMA, aiding in differential diagnosis.
• Microscopic examination post-amputation confirmed the diagnosis of pleomorphic rhabdomyosarcoma.

Implications:

• This case highlights the occurrence of pleomorphic rhabdomyosarcoma in rabbits, a condition rarely documented.
• Despite limb amputation and initial lack of detectable metastasis, the rabbit succumbed to metastatic disease 396 days post-surgery.
• The findings underscore the importance of thorough diagnostic workups, including immunohistochemistry, for accurate tumor characterization in rabbits and emphasize the potential for late-stage metastasis in such cases.