Epidemiologic Methodology in the Study of Feline Injection Site Sarcomas

Feline vaccine-associated sarcoma (FVAS) has been a continuing problem in the veterinary field since its first description in the early 1990s. Studies aimed at the pathology and treatment of FVAS have been conducted but there are few epidemiological studies that have been carried out. A prospective case-control study was conducted to compare vaccine and other injectable product risks of sarcomas in cats by employing a temporal and spatial approach for the evaluations, with validated time and location vaccination histories used to histologically distinguish feline vaccine versus nonvaccine-associated sarcomas. The aims were to demonstrate a methodologic design model for conducting future epidemiological studies of vaccine-associated sarcomas and to develop methods to differentiate sarcomas using different time-windows of vaccine history and body geographic information.;One study involving comparing and contrasting histological differences between vaccine-associated and nonvaccine-associated sarcomas showed areas of agreement with earlier published studies (increased inflammation, less differentiation, location in subcutis, enhanced presence of multinucleated giant cells, and increased numbers of lymphocytes), but also disagreement (lower mitotic indices, less nuclear pleomorphism, and less granulation tissue).;There were 90 cases reported in the broad interscapular region among which 47 cases had vaccine and injection information provided. There were 91 cases reported in the broad rear limb region among which 54 cases had vaccine and injection information provided. There were 96 controls with sarcomas at non-vaccine sites among which 44 controls had vaccine and injection information provided, and among 159 basal cell tumor controls, 96 controls had vaccine and injection information provided.;Exact logistic regression analyses (adjusted for age) contrasting the use of the three major vaccine types (inactivated, recombinant, and MLV) across all antigen classes in the broad interscapular region between cases with tumors located there and controls did not reveal any significant differences in the use of the different vaccine types regardless of whether they were administered within one, two, or three years prior to case or control diagnosis. The frequency of administration of long-acting corticosteroid injections (dexamethasone, methylprednisolone, and triamcinolone) was significantly higher in cases than the controls (P = 0.017) in this region.;There was statistical evidence of a higher frequency of use of inactivated rabies vaccines compared to the recombinant rabies vaccines in the broad rear limb region in year 1 through 3 (P = 0.003, P = 0.003 and P = 0.011, respectively). Exact logistic regression analyses (adjusted for age) results comparing cases with tumors located in this region and the three control groups suggested evidence of a significantly lower frequency of use of recombinant rabies vaccines in cases than controls. Using cats with non-vaccine site sarcomas as controls, in years one, two, and three, the odds ratios were: OR = 0.1, 95% CI = 0.0 -- 0.7, P = 0.014; OR = 0.1, 95% CI = 0.0 - 0.4, P = 0.001; and OR = 0.1, 95% CI = 0.0 -- 0.6, P = 0.005, respectively. Using cats with basal cell tumors as controls, the odds ratios in years one, two, and three were: OR = 0.1, 95% CI = 0.0 -- 0.4, P = 0.001; OR = 0.1, 95% CI = 0.0 - 0.4, P = 0.001; and OR = 0.1, 95% CI = 0.0 -- 0.6, P = 0.0004. Using the combined control group, the findings were: year one: OR = 0.1, 95% CI = 0.0 -- 0.4, P = 0.001; year two: OR = 0.1, 95% CI = 0.0 - 0.4, P < 0.0001; and year three: OR = 0.1, 95% CI = 0.0 -- 0.5, P = 0.0003).