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:
Doxorubicin (Adriamycin®) and Cyclophosphamide (Cytoxan®)
Vincristine (Oncovin®) and Cyclophosphamide (Cytoxan®)
Acemannan use has been tried for tumors less than 2 cm in diameter
The prognosis for this type of cancer depends on the location and stage of the tumor. For example, tumors on the tail, on the distal legs or that are small and localized have a very good prognosis. Tumors that are large and treated aggressively with radiation, surgery and chemotherapy still have a fairly good prognosis; however some cats can have either reoccurrence or metastasis. Cats that are treated with aggressive surgery at the first diagnosis have the best chance of survival. Ask your surgeon about the specifics about your cat's tumor.