GENERAL CONSIDERATIONS
+ Feline Vaccine-Associated Sarcomas
- Strong association between inactivated vaccines (i.e., FeLV and rabies) and STS at injection-sites
- Prevalence: 0.010%-0.036%, but may be as high as 0.1%
- Non-vaccine associated STS are uncommon in cats
- VAS develop in areas of inflammation induced by adjuvanted vaccine products
- VAS is histologically similar to traumatically-induced ocular sarcoma
- VAS odds increase by 50% after 1 vaccination, 127% after 2 vaccinations, and 175% after 3 vaccinations, but others have found no association with multiplicity of vaccinations
- VAS also reported at injection sites for anything that can cause local inflammation such as non-adjuvanted killed feline vaccines, lufenuron, corticosteroids, antibiotics, and microchips (due to hair follicles)
- VAS reported in series of cats receiving killed adjuvanted panleukopenia, rhinotracheitis, and calicivirus vaccine in Canada
- Interval between vaccination and VAS between 3 months and 3 years
- 2 proposed causes:
- Adjuvant rabies and FeLV vaccines have immunogenic adjuvants causing local and persistent inflammatory responses resulting in fibroblast and myofibroblast proliferation and neoplastic transformation
- Deposition of a high concentration of antigen
+ Vaccine Adjuvants
- Vaccine adjuvant is most commonly implicated as the cause of local tissue inflammation
- Aluminium (hydroxide or phosphate) is a common component of vaccine adjuvants and has been identified in post-vaccination granulomas and VAS
- Specific role of aluminium, other adjuvants, adjuvant components, and vaccine antigens is unknown
- Aluminium may only be a marker of previous vaccination and other vaccine components may induce or enhance inflammatory process resulting in sarcoma development
- Post-vaccination inflammatory reactions are common (80%-100%) although size of inflammatory lesions twice as large for rabies compared to 3 FeLV vaccines
- Adjuvant FeLV containing aluminium most consistently produces post-vaccination vaccine-site inflammation, whereas no inflammation is observed with non-adjuvanted FeLV vaccinations
+ Vaccination Site Inflammation
- Degree of inflammation is not reduced by administering vaccines intramuscular
- Post-vaccination inflammation resolves by 3 months
- Incisional biopsy is recommended for inflammatory mass > 2 cm in diameter or persisting > 4 months
- VAS and lymphocytes in VAS have a mild to strong reaction to PDGF and strongly express c-jun whereas non-VAS are not associated with either PDGF or c-jun
- Neoplastic cells in VAS closest to lymphocytes stain strongest for PDGF implying that lymphocytes in VAS may secrete PDGF, recruit macrophages, and cause myofibroblast proliferation
- No apparent association with FeLV or FeSV or papillomavirus or polyomavirus antigen and DNA
+ Pathology
- VAS have increased necrosis, inflammatory cells (lymphocytes and macrophages in particular), and mitosis compared to non-VAS
- VAS are mesenchymal in origin and can be FSA, malignant fibrous histiocytoma (or myofibroblastic sarcoma), OSA, CSA, leiomyosarcoma, undifferentiated sarcoma, lymphangiosarcoma, or rhabdomyosarcoma
- VAS are histologically similar to trauma-induced ocular mesenchymal tumors suggesting a similar pathologic mechanism of inflammation and wound healing
+ Vaccination-Associated versus Non-Vaccine-Associated Sarcoma
- VAS sites: interscapular, dorsolateral thoracic and flank, paralumbar, and femoral regions
- non-VAS sites: head (including oral cavity), limbs, bone, tail, and other
- VAS is diagnosed in 55% (94/170) cats with STS
- VAS, and not non-VAS, are associated with overexpression of PDGF, EGF, and TGF-β
+ Prevention
- Recommendations for prevention of VAS are controversial:
- Change vaccination sites
- Minimize use of polyvalent vaccines
- Use of non-adjuvant vaccines
- Avoid aluminium-based adjuvants
- Avoid over-vaccinating cats
- National Feline Vaccine-Associated Sarcoma Task Force states that no vaccine to be administered in the interscapular area with
- Rabies in the distal right pelvic limb
- FeLV in the distal left pelvic limb
- Other vaccines in the distal right thoracic limb
- Subcutaneous and intramuscular injections cause similar degree of inflammation and tumor production
- Subcutaneous sites are recommended as they are more easily detected
CLINICAL FEATURES
+ Signalment
- Mean age 8-12 years
- No sex or breed predilection
+ Clinical Signs
- Firm swelling at or near previous vaccination injection site < 3 years after vaccination
- Lymphadenopathy or respiratory distress due to metastatic disease is a rare presentation
+ Diagnosis
- FNA will differentiate abscess, granuloma, foreign body, and neoplasia
- Vaccine granulomas have reactive fibroblasts which can be difficult to differentiate from VAS
- Needle-core or incisional biopsy should be planned so biopsy tract can be removed with definitive procedure
- VAS have increased necrosis, inflammatory cells (especially lymphocytes, macrophages, and non-degenerate neutrophils ± reactive fibroblasts, eosinophils, mast cells, plasma cells, and multinucleate giant cells) and cycling cells compared to non-VAS
- Injection reaction is characterized by basophilic to azurophilic, amorphous, or globular intracytoplasmic material with macrophages or multinucleated giant cells
+ Imaging Studies
- Regional and thoracic radiographs for evidence of local invasion and metastatic disease
- Ultrasound, CT, or MRI is useful for determination of surgical margins or radiation field
- Tumor volume based on contrast-enhanced CT scans is approximately twice volume detected using palpation
TREATMENT
+ General Considerations
- Treatment options can be based on tumor size
- Small to medium-sized tumors: surgery (± adjunctive chemotherapy or immunotherapy)
- Large-sized tumors: radiation therapy or chemotherapy can be used to downsize tumor prior to surgical resection or, alternatively, surgery can be used to downstage VAS to microscopic disease for postoperative radiation therapy
+ Surgical Management
- Excisional biopsy is not recommended as seldom curative and recurrence results in more difficult 2nd surgery
- Interscapular location and infiltration makes surgical resection difficult even with partial scapulectomy and excision of epaxial muscles and dorsal spinous processes
- Amputation has a higher cure rate than surgery in the interscapular region
- Aggressive surgical resection is associated with recurrence rates of 30%-70% (despite complete excision)
- Local tumor recurrence usually observed within 6 months
- However, radical surgery with 3-5 cm lateral margins and 2 fascial layers deep (or body wall resection) has been reported in 30 cats with no evidence of local tumor recurrence with a mean follow-up time of 17.2 months
+ Radiation Therapy
- Radiation therapy is recommended because of difficulty in achieving complete excision and durable tumor control
- Adjuvant protocol: 3 Gy fractions Monday-Wednesday-Friday for 7 weeks with total 63 Gy or 2.7 Gy fractions Monday-to-Friday for 19-25 fractions
- Brachytherapy involves placement of radioactive sources into or near the tumor and results in high dose of radiation to the tumor bed while minimizing exposure and toxicity to surrounding tissue
+ Chemotherapy
- Chemotherapy has some beneficial effects in cats with VAS
- Doxorubicin, mitoxantrone, vincristine, and paclitaxel have in vitro activity against VAS-cell lines
- Doxorubicin (25 mg/m 2 or 1 mg/kg), carboplatin (200-240 mg/m 2), mitoxantrone, and cyclophosphamide have occasionally resulted in either PR or CR in cats with gross disease
- Doxorubicin alone is associated with a 39% overall response rate in cats with gross disease with 15% CR, 24% PR, and median response duration of 84 days
- Median DFI is significantly longer when cats with microscopic VAS are treated with doxorubicin (388 days v 93 days)
- Doxorubicin and cyclophosphamide result in 50% PR, but response duration is not durable with a median 125 days, however, MST for responders is significantly longer than non-responders (242 days v 83 days)
- However, doxorubicin did not improve survival time in cats treated with surgery and radiation therapy (674 days v 842 days)
+ Immunotherapy
- Non-specific immunomodulation (i.e., mixed bacterial vaccine or levamisole) has no effect on DFI or MST
- Acemannan may have some effect although small number of cats and used in combination with radiation therapy
- Acemannan causes macrophages to secrete more TNF-α, IL-1, PgE 2, and IFN, enhances macrophage phagocytosis and, through inhibition of glucosidase activity, may effect tumor cell adhesion and metastasis
- IL-2, combined with surgery and brachytherapy, significantly improves MST (16 months v 8 months), however, anaphylaxis is a problem with IL-2 administration
PROGNOSIS
+ General Considerations
- 0%-25% metastatic rate to lungs and other organs including skin, subcutaneous tissue, regional lymph nodes, mediastinum, liver, and pelvis
- p53 mutations are present in 20% (2/10) VAS and Mab-240, an anti-p53 antibody, was positive in 81% and cats with cytoplasmic expression of p53 have a significantly shorter DFI than those with nuclear expression of p53
- MMP 2 expression and lack of MT-MMP 16 expression and survival time are significantly correlated with a MST 822 days v 261-400 days if MMP 2 is not expressed or MT-MMP 16 is expressed
- poor prognostic factors include:
- Castrated male
- Large tumor size
1 surgery
- Incomplete excision
- Long interval between surgery and radiation therapy
- ± site (extremity longer survival time due to amputation and ability for complete resection)
- MST 345-576 days
+ Surgery
- Local tumor recurrence rate 25%
- Metastatic rate 25%
- Median DFI 10 months
- MST 345-576 days with a 1-year survival rate of 36.0% and 2-year survival rate 13.8%
- DFI is significantly influenced by VAS location, surgeon, completeness of histologic resection, and number of surgeries:
- Median DFI is significantly longer with tumors on the extremity than other sites (325 days v 66 days)
- Median DFI is significantly longer if 1st surgery is wide rather than marginal (325 days v 79 days)
- Median DFI for complete histologic resection is significantly longer than incomplete resection (> 16 months v 4 months)
- Median DFI is significantly longer following 1 surgery than ≥ 2 surgeries (> 16 months v 5 months)
- Median DFI 94 days if treated by general veterinarian or 272 days if referral surgeon
- MST is significantly influenced by surgeon, completeness of histologic resection, and number of surgeries:
- MST for complete histologic resection is significantly longer than incomplete resection (> 16 months v 9 months)
- MST is significantly longer following 1 surgery than ≥ 2 surgeries (16 months v 13 months)
+ Surgery and Radiation Therapy
- Local tumor recurrence rate 41%-45% and is significantly higher with > 1 surgery (31% v 55%)
- metastatic rate 12%
- median DFI 398-405 days
- Median DFI depends on the number of surgeries prior to radiation therapy and complete surgical resection:
- Median DFI is significantly greater with 1 surgery before radiation therapy (469 days v 345 days)
- Median DFI is significantly decreased with incompletely resected tumors (112 days v 700 days)
- MST 600-842 days with:
- 1-year survival rate 86%
- 2-year survival rate 44%
- 3-year survival rate 28%
- 4-year survival rate 24%
- 5-year survival rate 12%
- MST depends on sex and tumor size:
- Castrated males have a significantly shorter survival time than spayed females (638 days v 735 days)
- Large tumors prior to the 1st surgery have a significantly shorter survival time