[Written by a Veterinarian] What is Feline Fibrosarcoma? Symptoms, Causes, Treatments, and Daily Care

Have you ever felt anxious after finding a "hard lump" on your cat's body? One potential cause is feline fibrosarcoma. This is a malignant tumor that develops in the skin or subcutaneous tissue; if left untreated, it grows rapidly and is known for its high rate of recurrence. In this article, a veterinarian will provide an easy-to-understand explanation of the symptoms, causes, treatments, and daily care for this condition.

What is Feline Fibrosarcoma?

Characteristics of Fibrosarcoma

Fibrosarcoma is a malignant tumor that develops in a cat's skin, subcutaneous tissue, or muscles. It is a relatively common tumor in cats. It is typically discovered as a lump that feels firm to the touch; because it can be firmly attached to underlying tissues like muscle, it often does not move when touched. Fibrosarcoma is highly infiltrative, meaning it spreads into surrounding tissue, and is characterized by a very high recurrence rate even after surgical removal.

Affected Areas

While it can develop anywhere on the skin, it is most commonly found on the trunk or limbs. It can also occur at the site of injections, such as vaccinations.

Progression and Recurrence

Fibrosarcoma is a tumor with a very high potential for local infiltration and recurrence. Local infiltration means that tumor cells spread into the tissues surrounding the growth, which is why surgical removal must include a wide margin of normal tissue along with the tumor itself. If the tumor is not completely removed, recurrence is common shortly after surgery, and it can sometimes recur even if pathology reports indicate that clean margins were achieved.

Symptoms of Feline Fibrosarcoma

Hard Lumps on or Under the Skin

Fibrosarcoma often forms in the skin or subcutaneous tissue and can be felt as a firm, knot-like lump. While benign tumors are typically movable and not firmly attached to surrounding tissue, fibrosarcomas are characterized by being fixed in place and difficult to move.

Rapid Growth of the Mass

Unlike benign tumors, which often stay the same size over time, the malignant fibrosarcoma is highly infiltrative and spreads into neighboring tissues, causing it to grow as time passes.

Ulceration and Bleeding

As the tumor grows, the surface may develop ulcers or start to bleed.

Systemic Illness and Loss of Appetite

If a fibrosarcoma develops on a limb, it can cause severe pain, leading to a decrease in appetite. While this tumor does not often metastasize, it can spread to the lungs, potentially causing difficulty breathing due to pleural effusion.

Causes and Risk Factors

Connection to Vaccinations and Injections (Injection-Site Sarcoma)

Although very rare, tumors can develop following a vaccination or injection. Because they occur at the site of the injection, they are referred to as "injection-site sarcomas," but are classified as fibrosarcomas. If you notice a lump at an injection site that "has been growing for over a month," "is larger than 2cm," or "is still present after 3 months," it may be a fibrosarcoma. Quadrivalent vaccines, including those for feline leukemia virus, are thought to be potential triggers for these sarcomas.

Chronic Inflammation or Irritation

While the exact cause of fibrosarcoma is not fully understood, chronic inflammation or irritation may be a contributing factor. Stimuli from vaccines or medications are thought to induce persistent inflammation. Injuries can also be a cause; in one case I previously encountered, a fibrosarcoma developed around the site of a prior hind-leg fracture, although a clear causal relationship remains unproven.

Risk in Middle-Aged and Older Cats

Feline fibrosarcoma occurs most frequently in middle-aged and older cats. No specific breed is known to be more susceptible than others.

Treatment and Prognosis

Surgery

Because fibrosarcoma is prone to recurrence, it must be completely excised. Due to its high local infiltrative nature, surgery requires removing not just the tumor, but also a wide margin of normal tissue. It is necessary to remove normal tissue at least 2–3 cm away from the tumor site, including the underlying muscle. While complete removal can lead to a cure, the high risk of recurrence from even the smallest amount of leftover cells makes the initial surgery the key to success.

Because many fibrosarcomas develop on the limbs, amputation is often chosen as a treatment option, as it offers a very high probability of a complete cure.

Radiation Therapy and Chemotherapy

Fibrosarcoma progresses rapidly and roots itself into nearby tissues. Even with wide-margin surgery, there are cases where the tumor cannot be completely removed. In such instances, chemotherapy or radiation therapy may be used. However, these therapies are generally ineffective on their own and are typically used to shrink the tumor before surgery or to prevent recurrence after surgery.

High Recurrence Risk: Early Detection and Treatment Lead to Better Prognosis

Fibrosarcoma progresses quickly and can recur even after surgical removal. If the tumor is caught while still small, there is a good chance for a complete recovery through wide-margin excision. Early detection and treatment are vital.

Daily Care and What Owners Can Do

The Habit of Checking for Lumps

Fibrosarcoma is a tumor that feels firm to the touch. While they can develop at vaccination or injection sites, they can certainly appear elsewhere as well. Make it a habit to regularly touch your cat's body to check for lumps. If you notice any discomfort, especially at an injection site, consult your veterinarian immediately.

Regular Health Screenings

Physical exams during regular health checkups often include palpation, which may reveal a lump. Especially in middle-aged and older cats, the risk of various tumors and other illnesses increases. Aim to have health checkups at least twice a year.

Post-Operative Support

Treating fibrosarcoma requires wide-margin excision. If the tumor is on a limb, amputation may be chosen. While cats can adapt well to life after amputation, they may struggle with balance for a while, so you should adjust your home environment to prevent accidents. Additionally, because a large area is removed, the wound will be significant. Sudden movements or contact with other pets could cause the wound to reopen, so your cat should be kept calm until the stitches are removed.

Fibrosarcoma can also develop in the mouth. In these cases, the jawbone may need to be removed, which might necessitate the use of an esophageal or gastric feeding tube. The cat's diet will also require special attention.

Summary: Facing Feline Fibrosarcoma

Fibrosarcoma is a fast-progressing tumor that quickly invades surrounding tissues. It has a high rate of recurrence, meaning it can come back even after surgical removal. To prevent recurrence, it must be excised widely while the tumor is still small. If completely removed, it is possible for the cat to live without recurrence. Please make it a habit to check your cat's body regularly to help ensure early detection.