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

Have you ever been worried after finding a "hard lump" on your cat's body? One of the possible causes is feline fibrosarcoma. This is a malignant tumor that develops in the skin or subcutaneous tissue, and if left untreated, it can grow rapidly. It also has a high recurrence rate. In this article, a veterinarian will provide an easy-to-understand explanation of its symptoms, causes, treatments, and daily care.

What is Feline Fibrosarcoma?

Characteristics of Fibrosarcoma

Fibrosarcoma is a malignant tumor that develops in the skin, subcutaneous tissue, and muscles of cats. It is a relatively common tumor in cats. It is discovered as a lump, but it feels hard to the touch and often does not move when touched because it is fixed to muscles or other tissues. Fibrosarcoma is characterized by its high invasiveness, spreading to surrounding tissues, and a very high recurrence rate even after surgical removal.

Location of Occurrence

While it can occur anywhere on the skin, it is commonly observed on the trunk and limbs. It can also develop at the site where vaccines or other injections were administered.

Progression and Recurrence Rate

Fibrosarcoma is a tumor with very high local invasiveness and recurrence risk. Local invasiveness means that tumor cells spread to the surrounding tissues, so the surgical removal of fibrosarcoma requires wide excision, including normal tissue around the tumor. If the tumor is not completely removed, recurrence is often observed after surgery, and it can recur even if pathological examination indicates complete removal.

Symptoms of Feline Fibrosarcoma

Hard Lump on Skin or Subcutaneous Tissue

Fibrosarcoma often develops in the skin or subcutaneous tissue and feels like a firm, hard lump. While benign tumors typically don't adhere much to other tissues and have some mobility when touched, fibrosarcoma is characterized by its adherence to other tissues and limited movement.

Rapid Growth of the Tumor

Unlike benign tumors, which do not change much in size over time, fibrosarcoma, being a malignant tumor, is highly locally invasive and spreads to surrounding tissues. It is characterized by its growth over time.

Ulceration and Bleeding May Also Occur

As the tumor grows, ulcers may form on its surface, and bleeding can occur from these sites.

Poor Health and Loss of Appetite as It Progresses

If fibrosarcoma develops on a limb, it can cause severe pain, which may lead to a decrease in appetite.
Although this tumor rarely metastasizes, it can spread to the lungs, causing respiratory distress due to pleural effusion.

Causes and Risk Factors

Association with Vaccines and Injection Sites (Injection Site Sarcoma)

Very rarely, a tumor can develop after a vaccine or injection. Because it occurs at the injection site, it is also called "injection site sarcoma," but it is classified as fibrosarcoma. If a lump at the injection site "grows for more than one month," "is larger than 2 cm," or "remains for three months," it may be fibrosarcoma. The 4-in-1 vaccine, including feline leukemia virus, is thought to be a cause of fibrosarcoma.

Chronic Inflammation and Irritation

While the exact cause of fibrosarcoma is not fully understood, chronic inflammation or irritation may be contributing factors. Irritation from vaccines or medications is thought to sustain inflammation. Injuries can also sometimes cause fibrosarcoma. I have experienced cases where fibrosarcoma developed around a fractured hind leg, although a clear causal relationship remains unknown.

Risk of Onset in Middle-Aged and Older Cats

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

Treatment and Prognosis

Surgery

Fibrosarcoma is a tumor with a high recurrence rate, so it must be completely removed. Due to its strong local invasiveness, surgical removal requires excising not only the tumor itself but also a margin of healthy tissue. It is necessary to remove normal tissue at least 2 to 3 cm away from the tumor and also the muscle tissue beneath the tumor. If completely removed, there is a possibility of cure. However, if even a small amount is left behind, the recurrence rate increases, so the initial surgery is key to success.

Since fibrosarcoma often develops in the limbs, amputation is often chosen as a treatment because it offers a very high chance of complete cure.

Combination with Radiation Therapy or Chemotherapy

Fibrosarcoma progresses rapidly and deeply roots itself in nearby tissues. While surgical removal involves excising a wide area of tissue distant from the tumor cells, there are cases where it cannot be completely removed. In such instances, chemotherapy or radiation therapy may be used in combination. However, chemotherapy and radiation therapy alone have limited effectiveness and are generally used to shrink the tumor before surgery or to prevent recurrence after surgery.

Early detection and treatment improve prognosis due to high recurrence rate

Fibrosarcoma progresses rapidly, and even if it is surgically removed, it can recur. If the tumor is small, there is hope for a complete cure with wide excision. Early detection and early treatment are crucial for fibrosarcoma.

Daily Care and What Owners Can Do

Habit of Checking for Lumps by Touching the Body

Fibrosarcoma is a firm, hard tumor. While it can occur in areas where vaccines or injections have been given, it can also develop elsewhere. Regularly check your cat's body for lumps. If you notice any abnormalities, especially in areas where vaccines or injections were administered, consult a veterinarian.

Regular Health Check-ups

During a health check-up, the veterinarian will physically examine your cat, which might reveal a lump. Especially in middle-aged and older cats, the incidence of tumors other than fibrosarcoma and other diseases increases. It is recommended to have regular health check-ups, for example, twice a year.

Post-operative Life Support

Treatment for fibrosarcoma requires the extensive removal of the tumor, including surrounding tissues. If it occurs in a limb, amputation may be chosen. While cats can generally adapt well to life after amputation, they may experience temporary balance issues. It's important to adjust their environment to prevent accidents. Additionally, since a wide area is excised, the wound will be large. Strenuous activity or contact with other cats could cause the wound to open. After surgery, keep your cat calm until the stitches are removed.

Fibrosarcoma can also occur in the mouth. In such cases, part of the jawbone might need to be removed, and the cat may need to be fed through an esophageal or gastric tube. Careful attention to diet is also necessary.

Summary: Facing Feline Fibrosarcoma

Fibrosarcoma progresses rapidly and invades nearby tissues. It has a high recurrence rate, even after surgical removal. To prevent recurrence, it is necessary to excise a wide area while the tumor is still small. If completely removed, a recurrence-free life is possible. To ensure early detection, make it a habit to regularly check your cat's body.