Injection-Site Sarcoma (Vaccine-Site Sarcoma) in Cats

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Treatment of Injection-Site Sarcoma (Vaccine-Site Sarcoma)

Because of the aggressive nature of the injection-site sarcoma, no single treatment has proved effective. However, treatment may include one or more of the following:

  • Surgical excision
  • Radiation therapy
  • Chemotherapy

    Home Care

    The most important thing you can do at home is to observe the area of concern carefully. Record when you first noticed the mass and seek advice from your veterinarian.

    Regular visits to your veterinarian are critical to monitor your cat and treat this problem if it arises. Your veterinarian will examine the mass, measure and record its size and location, and discuss biopsy procedures with you.

    After a veterinary pathologist has examined the biopsy specimen and given a diagnosis, appropriate treatment can be discussed and implemented by your veterinarian.

  • Preventative Care

    The only prevention is to eliminate vaccinations. However, since the incidence of injection-site sarcomas is low, it is wise to continue your immunization schedule. Consider vaccination every 3 years (rather than yearly) for rabies and panleukopenia. Limit vaccination for FeLV (feline leukemia virus) and FIP (feline infectious peritonitis) to at-risk cats as needed.

    After immunizations, monitor your cat for swellings that may develop in body regions of previous injection or vaccination and see your veterinarian as soon as possible for early diagnosis and treatment.

    In-depth Information on Vaccine-Assocaited Sarcoma in Cats

    Other conditions both benign and malignant can occur and are often confused with injection-site sarcoma. Following is a partial list of such swellings:

  • Subcutaneous abscess – a localized collection of pus in a cavity formed by the disintegration of tissue that is common in cats that roam and fight with other cats.
  • Infectious granuloma – an inflammatory mass associated with unusual bacteria or fungal infectious agents
  • Sterile granuloma – cat an inflammatory mass associated with administration of certain medications under the skin.
  • Panniculitis – cat the inflammation of the subcutaneous tissue
  • Steatitis – cat inflammation of subcutaneous fat
  • Epidermal inclusion cyst – cat a cyst in the outermost layer of skin derived from a hair follicle that has accumulated debris or fluid
  • Pilomatrixoma – benign tumor of the hair follicle
  • Sebaceous gland adenoma – cat a benign tumor of the glands that empty into the hair follicle
  • Other benign tumors
  • Chondrosarcoma – cat a malignant tumor derived from cartilage cells
  • Malignant fibrous histiocytoma – malignant tumor derived from tissue cells called histiocytes.
  • Mast cell tumor – malignant tumor derived from inflammatory tissue cells called mast cells
  • Lymphosarcoma – malignant tumor derived from immune cells called lymphocytes
  • Osteosarcoma – malignant tumor derived from bone cells
  • Rhabdomyosarcoma – malignant tumor derived from muscle
  • Sebaceous gland adenocarcinoma – malignant tumor derived from glands that empty into hair follicles
  • Apocrine gland adenocarcinoma – malignant tumor derived from sweat glands
  • Other malignant tumors
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    Diagnosis In-depth

    Diagnostic tests must be performed to confirm the diagnosis of injection-site sarcoma and exclude other types of masses. Tests may include:

  • A complete medical history and physical examination
  • Tests may be required to determine the nature of a swelling and the risk of distant spread (metastasis). For example, X-rays of the chest may be taken to evaluate for spread of a tumor to the lungs. Routine blood and urine tests may be completed to determine your pet’s general health and ability to safely tolerate sedation or anesthesia for biopsy or removal of the mass.
  • Injection-site sarcomas can be diagnosed by history of vaccination and occurrence of a mass in a region of the body where vaccination has been performed. Biopsy of any mass that has developed in an area of previous injection or vaccination is recommended. The location, shape and size of the mass should be determined and recorded.
  • Radiographs. X-rays of the chest or nearby area of bone is often recommended to determine if any metastasis has occurred.
  • Advanced imaging. CT or MRI scans may be recommended to help determine the full extent of the tumor. Many tumors have root-like projections that extend further than the palpable mass. The best treatment success requires a full understanding of the extent of the tumor. 
  • Treatment In-depth

    The current recommendations for management of injection-site sarcomas are as follows:

    Consider any mass that develops in the area of a previous injection or vaccination to be malignant until proven otherwise. A mass should be treated aggressively if it meets the following criteria:

  • Persists for 3 months or more
  • Is larger than 2 cm (just under 1 inch) in diameter
  • Is increasing in size one month after injection or vaccination

    If the lesion meets one or more of these criteria, a biopsy is recommended before surgical excision. A biopsy is a procedure in which a small portion of the mass is removed and sent to a laboratory for microscopic examination by a veterinary pathologist. Biopsy samples can be collected by a special biopsy needle (called a Tru-Cut® needle) or by surgical incision of the mass to obtain a small wedge of tissue for microscopic examination. Fine needle aspiration and cytological examination using a conventional syringe and needle is not recommended because tumors of the sarcoma type generally do not readily shed cells during this procedure. Sedation or anesthesia may be required to obtain the biopsy sample.

    Tumors typically are firm, well-demarcated, and gray to white in appearance. Many tumors are 4.0 cm (about 1 1/2 inches) in size when first noticed.

    If the diagnosis of neoplasia (cancer) is determined by microscopic examination of the biopsy specimen:

  • The cat should be evaluated for distant spread of the tumor (metastasis). The initial evaluation can be completed by your veterinarian but more specialized procedures like computed tomography will require referral to a veterinary specialty clinic or university veterinary teaching hospital.

    Diagnostic procedures to evaluate for metastasis include:

  • Chest X-rays to evaluate for any masses that may have spread to the lungs
  • Computed tomography (CT) or magnetic resonance imaging (MRI) are imaging techniques that provide images of computer-generated “slices” through a patient’s body. If necessary, these tests require referral to a veterinary specialty clinic or university veterinary teaching hospital. Some sarcomas spread along the tissue planes that cannot be adequately evaluated by palpation or routine X-rays. These sophisticated imaging tests can be very useful to determine the extent of the mass and to evaluate the area that may require radiation treatment.
  • Routine blood tests and urinalysis may be recommended to identify co-existing medical conditions that may alter recommendations for anesthesia and treatment.

    Treatment of injection-site sarcomas must be individualized based on the extent of the mass, distant spread of the tumor (metastasis) and other factors that must be analyzed by your veterinarian. Treatment options include some combination of surgery, radiation treatment and chemotherapy. Currently, no cure for injection-site sarcomas exists, and research is ongoing regarding the best recommendations for prevention and treatment.

    Treatment recommendations may include:

  • Consultation with a veterinary oncologist before initiating therapy. Such consultation will help determine the best approach for your pet and will identify any need for specialty referral, such as for extensive surgery, radiation therapy, or chemotherapy.
  • Surgical removal of the tumor. You may be referred to a specialist in veterinary surgery if an extensive or complicated procedure is deemed necessary. The removed mass should be submitted for microscopic examination by a veterinary pathologist to determine if the entire mass was removed. Routine surgical recommendations include handling the tumor carefully to avoid any potential spread and performing a very wide excision (removal) of the tumor to try and remove all of the small finger-like projections that may extend into surrounding tissues. Recurrence is common, and it is recommended to remove at least 2 cm of healthy tissue around all sides of the tumor. This may involve very aggressive surgical techniques, including reconstruction of the body wall and removal of bone. The best treatment success involves very aggressive surgery at time of initial diagnosis by a surgeon.
  • Amputation of an involved limb. It is recommended that the surgeon mark the location of the mass in the event that the pathologist reports tumor cells “in the margins” of the submitted sample and a second surgery is required. Complete surgical excision of low-grade tumors may result in survival times of 16 to 24 months.
  • Radiation treatment is recommended before surgery in some cases to try and minimize tumor size and after surgery in some cases if the surgical removal is thought to have been incomplete.
  • Chemotherapy may be recommended for non-resectable tumors but is likely to be of limited benefit.
  • A complete blood count (CBC) and platelet count will be recommended prior to each chemotherapy treatment to evaluate for drug toxicity.
  • Chemotherapy protocols for injection-site sarcomas vary based on the experience of the veterinary oncologist.

    Recommendations may include the following drugs:

  • Carboplatin
  • Doxorubicin (Adriamycin®) and Cyclophosphamide (Cytoxan®)
  • Vincristine (Oncovin®) and Cyclophosphamide (Cytoxan®)
  • Ifosfamide
  • Acemannan use has been tried for tumors less than 2 cm in diameter
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