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There is epidemiologic evidence of strong association between administration of inactivated organism vaccines and subsequent development of soft issue sarcomas at vaccine sites in cats. The prevalence of soft tissue sarcomas after vaccination varies between 1/1,000 and 1/10,000 cats. If these prevalences are to be applied to the 1991 cat population of the United States, a total of 22,000 vaccine-induced tumors developed in 1991. Recommendations for preventing or decreasing the prevalence of vaccine-associated sarcomas in cats are controversial, and among others, include changing vaccination site location, decreasing use of polyvalent vaccines, using nonadjuvanted vaccines, avoiding use of aluminum-based adjuvants, and avoiding overvaccination.
The most important recommendation for prevention of vaccine-associated tumors would appear to be not overvaccinating. Kass et al clearly documented that the risk of vaccine-associated tumors increases with the number of vaccines administered. It is also clear from recently published article by Scott et al that the duration of immunity of many of the commercially available vaccines for cats is more than 1 year, and an every-3-year program should be instituted for many vaccines containing infective agents of cats. With respect to rabies vaccination, annual vaccination against rabies by use of a 3-year rabies product should be discouraged (ie, for fear of malpractice). The indiscriminate use of FeLV vaccine should be stopped because epidemiologic data suggest that it is the number 1 cause of vaccine-associated sarcomas in cats. Few veterinarians now recommend FeLV vaccination for strictly indoor cats.
Vaccine site location recommendations have also changed. The Vaccine-Associated Feline Sarcoma Task Force studying vaccine site tumors recommends that no vaccine be given in the interscapular space, that rabies vaccine be administered in the distal portion of the right hind limb, that FeLV vaccine be administered in the distal portion of the left hind limb, and that all other vaccines be administered in the right shoulder region. It appears from our research and reports by others that IM and SC administration results in local inflammation and tumor induction. Subcutaneous sites are recommended for all vaccines because that will ensure earlier detection of these growths. The reasoning behind recommending these vaccine administration sites is not based as much on prevention, but rather on earlier diagnosis, potentially leading to a higher cure rate when surgical treatment is selected.
The issue of monovalent and polyvalent vaccines is still controversial. Kass et al (2)found a significant positive trend in risk with increasing number of vaccines given. However, Hendrick et al (1)did not find an association between vaccination and nonvaccination site tumors in the number of vaccinations given simultaneously. Although ambiguity exists, it seems prudent to recommend that vaccines be administered at different sites and to not use polyvalent vaccines.
Use of vaccines containing aluminum-based adjuvants is controversial. The recommendation to not use multiple dose vials for aluminum-adjuvanted vaccines appears less controversial. Aluminum-adjuvanted products are the most consistent inducer of vaccine site inflammation and, in our opinion, should be avoided if possible. However, nonaluminum-based adjuvants have also been linked to tumor production, and may be equally unsafe. In 1985, we traded a modified live rabies virus vaccine that caused problems in 1/500,000 cats for a killed virus adjuvanted vaccine that induced tumors in 1/1,000 cats (boy, were we smart! ).
It would appear that the problem of vaccine-associated sarcomas will be with us for some time, and the question of what to do with postvaccination lumps is a real one. Some rabies and FeLV vaccines are associated with postvaccinal lumps in 100% of the vaccinates but, fortunately, most lumps go away in 2 to 3 months. Few vaccine-associated tumors develop sooner than 3 months after vaccination. Given these facts, we recommend that any vaccine-site lumps detected after 3 months following the time of vaccination he biopsied and, if malignant, be surgically excised. An incisional biopsy will determine magnitude of the surgery (ie, lumpectomy vs aggressive surgery). Attempts at simple excision of these tumors are seldom curative and ultimately lead to local recurrence and a more difficult second attempt. Even attempts at aggressive wide surgical excision are often incomplete and result in a 30 to 70% failure rate There appears to be an advantage to referring these cats to a qualified surgeon before the second surgery is contemplated. Hind limb amputation has a higher rate of cure than does surgery in the interscapular space for vaccine-associated sarcomas.
Given the incomplete removal of these tumors even by use of aggressive surgery, radiation therapy is often used either before or after surgery. Although the combination of surgery and radiation therapy has increased tumor control rate, a high number of cats still fail to undergo a cure when this combination its used. Several chemotherapy agents, including carboplatin, doxorubicin, mitoxantrone, cyclophosphamide, and vincristine, have been used in cats with vaccine-associated tumors. Use of most chemotherapeutic protocols results in a partial response, but some responses are complete. Combinations of doxorubicin (25 mg/m2 of body surface area, IV, on day 1 of a 21 day cycle) and cyclophosphamide (200 to 300 mg/m2, PO, on day 10 of the cycle), mitoxantrone (4 to 6 mg/m2, IV, on day 1 of a 21-day cycle) and cyclophosphamide (200 to 300 mg/m2, PO, on day 10 of the cycle), or single agent carboplatin (250 mg/m2, IV, every 3 to 4 weeks) have resulted in some partial and complete remissions; however, sarcomas in cats are not very chemoresponsive. Although most vaccine associated tumors are only locally invasive, approximately 10 to 25% metastasize to the lungs, eyes, or other sites. The cost of these treatments can be high and may run into many thousands of dollars. The ethics of the profession and how we manage this problem are being watched by many, including the media. How we act on this issue is likely to have a profound effect on how our profession is perceived by the public for some time in the future.
Given the need for vaccination against rabies to prevent a lethal disease in cats and human beings, there would appear to be a need to compensate owners for expenses associated with treatment of tumors that develop after administration of mandated vaccines such as rabies. Perhaps it is time that the veterinary profession consider a vaccine injury act similar to the 1986 Childhood Vaccine Injury Act in use for human beings injured by mandated vaccines, such as the diphtheria/pertussis/tetanus and measles/mumps/rubella vaccines. More legislative support is also needed and required in truth-in-labeling of animal vaccines that have been associated with vaccine site sarcoma development. Currently, a 3-year rabies vaccine may be relabeled as a 1-year rabies vaccine. Currently, annual revaccination for FeLV is recommended, without any evidence of duration of immunity.
From the Department of Clinical Sciences, College of Veterinary Medicine, The Ohio State University, Columbus, OH 43210 (Couto), and Comparative Oncology Unit, Department of Clinical Sciences, College of Veterinary Medicine, Colorado State University Fort Collins,CO 80523 (Macy)
References
1. Hendrick MJ, Shofer FS, Goldschmidt MH, et al. Comparison of fibrosarcomas that developed at vaccination sites and at nonvaccination sites in cats: 239 cases (1991-1992). J Am Vet Med Assoc1994;205:1425-1429.
2. Kass PH, Barnes WG Jr, Spangler WL, et al. Epidemiologic evidence for a causal relation between vaccination and fibrosarcoma tumorigenesis in cats. J Am Vet Med Assoc1993;203:396-405.
3. Lester S, Clemett T, Burt A. Vaccine site-associated sarcomas in cats: clinical experience and a laboratory review (1982-1993): J Am Anim Hosp Assoc1996;32:91-95.
4. Scott FW, Geissinger C. Duration of immunity in cats vaccinated with an inactivated feline panleukopenia, herpesvirus, and calicivirus vaccine. Feline Pract 1997;25:12-19.
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