Vaccine-Associated Feline Sarcoma Task Force Guidelines - Diagnosis and Management of Suspected Sarcomas

The following recommendations are based on information available as of April 1999 and are subject to revision as new information becomes available.


  1. Record anatomic location, shape, and size (measured by caliper and recorded in three dimensions) of all masses that occur at the site of an injection.
  2. Manage a mass that develops at a previous injection site as if it were malignant until proven otherwise. A lesion should be fully assessed and aggressively treated if it meets any one of the following criteria:
    • Persists more than 3 months post-injection
    • Is larger than 2 cm in diameter
    • Is increasing in size after one month post-injection
  3. If a mass meets one or more of the above criteria, we recommend that you perform a diagnostic biopsy prior to surgical excision. A tru-cut needle biopsy or incisional wedge biopsy is preferred for diagnosing lesions. Tru-cut biopsy should be done in such a way that subsequent surgical removal can readily include the entire needle tract. Wedge biopsy should be performed so that subsequent surgery can remove all tissue affected by the biopsy. Fine needle aspiration cytology is considered unreliable for the diagnosis of vaccine-associated feline sarcomas (VAFS) and is not recommended.


Masses confirmed as malignant should be handled as listed below:

  1. Perform routine thoracic radiographs and pre-operative lab work for any malignant mass.
  2. When feasible, cats with histologically confirmed VAFSs should be imaged by computerized tomography (CT) or magnetic resonance imaging (MRI). Soft-tissue sarcomas often spread along fascial planes and may be undetectable visually in early stages of tumor growth. Advanced imaging data are very useful in determining the extent of surgery and/or the size of the radiation field that will be needed to maximize the chances for successful treatment.
  3. Consult with an oncologist for current treatment options, which may include radiation, chemotherapy, surgery, or other modalities, prior to initiating therapy.
  4. Never "shell out" a sarcoma. Incomplete surgical removal of a sarcoma is the most common cause of treatment failure. Employ oncologic surgical techniques to avoid seeding malignant cells. Remove at least a 2-cm margin in all planes, including the deep side. In some instances, this will involve reconstruction of the body wall, removal of bone, or other advanced surgical techniques.
  5. Submit the entire excised specimen for histopathology. Mark the excised mass with India ink or suture tags to provide an anatomical reference to facilitate subsequent treatment.
  6. Report all histologically confirmed VAFSs to the manufacturer and to U.S. Pharmacopoeia Veterinary Practitioners' Reporting Program. To make a report or request reporting forms, call 800-4-USP-PRN (800-487-7776) or visit the USP Web site at

After a sarcoma has been removed:

  1. Recheck by physical examination monthly for the first three months, then at least every 3 months for one year.
  2. Perform additional diagnostic procedures as appropriate for the abnormalities detected.