Vaccine-associated fibrosarcoma with keloidal differentiation in a cat

Area of Science:

• Veterinary Oncology
• Feline Pathology
• Vaccine-Associated Neoplasia

Background:

• Feline Leukemia Virus (FeLV) vaccines are crucial for preventing a common retroviral infection in cats.
• While generally safe, vaccine-associated adverse events, including injection-site tumors, are a recognized concern.
• Understanding the specific types and characteristics of these tumors is vital for feline health management.

Observation:

• A 6-year-old Domestic Shorthair cat presented with a slow-growing subcutaneous mass on its left hind limb.
• The mass appeared approximately 16 months after the cat received Feline Leukemia Virus (FeLV) vaccinations.
• The mass's location corresponded to a typical vaccination site.

Findings:

• Histopathological and immunohistochemical examinations confirmed the subcutaneous mass as a fibrosarcoma.
• The fibrosarcoma exhibited keloidal differentiation, a less common feature in these tumors.
• The tumor's development timeline and location strongly suggested a link to prior Feline Leukemia Virus (FeLV) vaccinations.

Implications:

• This case underscores the importance of monitoring injection sites for persistent or growing masses in cats post-vaccination.
• The diagnosis of vaccine-associated fibrosarcoma with keloidal differentiation provides valuable data for veterinary oncologists and pathologists.
• Further research into the mechanisms of vaccine-associated sarcomagenesis in felines may inform future vaccine development and administration protocols.