Feline fibrosarcoma is an aggressive cancer originating in the fibrous connective tissues of cats. This malignant tumor often affects the skin or subcutaneous tissues, appearing in various body locations. Recognizing potential signs and seeking timely veterinary attention is important for cat owners.
What is Feline Fibrosarcoma?
Fibrosarcoma is a soft tissue sarcoma developing from fibroblasts, the cells that create connective tissue. These tumors are locally aggressive, extensively infiltrating surrounding tissues. Though uncommon, they are highly invasive.
These masses most frequently appear in or just beneath the skin, known as subcutaneous fibrosarcomas. Common sites include the back, shoulder blades, limbs, head, and neck. While locally aggressive and fast-growing, their tendency to spread to distant organs like the lungs or lymph nodes is relatively low, occurring in less than 25% of cases.
Recognizing the Signs
The most noticeable sign of feline fibrosarcoma is a firm lump or mass under the cat’s skin. This lump often feels fixed to underlying tissues and can grow quickly, though it may not be painful initially.
Lumps vary in size and appearance, potentially ulcerating or bleeding if untreated. Owners might also observe hair loss or skin color changes over the affected area. Tumors in the mouth or nasal passages can cause difficulty eating, drooling, bad breath, sneezing, or nasal discharge. Regular physical checks help detect new or changing lumps early.
Understanding the Causes
A prominent cause of feline fibrosarcoma is its association with certain injections, known as Vaccine-Associated Sarcoma (VAS) or injection-site sarcoma. Inflammation at the injection site, possibly from vaccine adjuvants, can trigger abnormal cell growth. Rabies and feline leukemia virus (FeLV) vaccines are most commonly implicated, though the risk is rare (approximately 1 in 10,000 to 30,000 vaccinations).
These tumors can develop months or years post-vaccination, typically appearing between three months and four years. Other less common factors contributing to fibrosarcoma development include genetic predispositions, chronic inflammation, or, rarely, the feline sarcoma virus (FeSV), a mutant FeLV form causing multiple, fast-growing tumors in younger cats.
Diagnosis and Treatment Approaches
Diagnosis begins with a thorough physical examination and assessment of suspicious lumps. Initial steps involve a fine needle aspirate (FNA) to collect cells for microscopic examination. A definitive diagnosis typically requires a tissue biopsy for comprehensive tumor information. Imaging studies (X-rays, CT, MRI) determine tumor size, local invasiveness, and spread to areas like lungs or lymph nodes.
Surgical removal is the primary and most effective treatment. Due to the tumor’s invasive nature, surgeons remove the visible mass with a significant margin of healthy tissue (often 3-5 cm in all directions and at least one fascial plane deep). For limb tumors, amputation may be recommended to achieve adequate margins and improve the chance of a cure.
Adjunctive therapies are often combined with surgery to reduce recurrence risk. Radiation therapy can be given before surgery to shrink the tumor or after to eliminate remaining cancer cells. This includes conventional fractionated radiation (CFRT) or stereotactic radiation (SRS), which delivers higher doses in fewer sessions. Chemotherapy is generally not the primary treatment due to variable effectiveness, but may be considered for aggressive tumors, to slow growth, or manage potential distant spread, though its role in preventing metastasis is debated.
Prevention and Long-Term Care
Proactive measures can reduce vaccine-associated fibrosarcoma risk. Veterinarians recommend administering vaccines in specific, easily accessible sites like distal limbs or the tail, allowing for simpler surgical removal if a tumor develops. Rotating injection sites and considering non-adjuvanted vaccines also minimize inflammation.
Long-term care involves diligent monitoring for recurrence, as fibrosarcomas often return. Regular veterinary check-ups are important for early detection of new lumps or changes. Owners should routinely feel their cat’s body for unusual masses. Prompt veterinary attention for suspicious findings is essential for effective disease management and improved long-term outcome.