Adjuvant immunotherapy of feline injection-site sarcomas with the recombinant canarypox virus expressing feline interleukine-2 evaluated in a controlled monocentric clinical trial when used in association with surgery and brachytherapy

The objective of this randomised, controlled, parallel-group monocentric clinical trial was to assess the efficacy (at low and high dose) and the safety (at high dose) of a recombinant canarypox virus (ALVAC®) expressing feline interleukin 2 (IL-2). ALVAC IL-2 was administered to cats as an adjunct treatment of feline fibrosarcoma in complement to surgery and brachytherapy (reference treatment). Seventy-one cats with a first occurrence of feline fibrosarcoma were referred to the Veterinary Oncology Centre for post-surgical radiotherapy. They were randomly assigned to three treatment groups: reference treatment group (23 cats), ALVAC IL-2 low dose group (25 cats) and ALVAC IL-2 high dose group (23 cats). Two dosages of ALVAC IL-2 were used to assess both safety (high dose) and efficacy (high and low doses). The treatment consisted of six consecutive doses of ALVAC IL-2 administered subcutaneously at the tumour site on Day 0 (one day before brachytherapy treatment), Day 7, Day 14, Day 21, Day 35 and Day 49. All cats were evaluated for relapse (i.e. local tumour recurrence and/or metastasis) every three months for at least one year (ALVAC IL-2 high dose group) or two years (reference treatment and ALVAC IL-2 low dose groups) by complete physical examination and regular CT scans. ALVAC IL-2 treatment was well tolerated and adverse effects were limited to mild local reactions. ALVAC IL-2 treatment resulted in a significant longer median time to relapse (>730 days in the ALVAC IL-2 low dose group) than in the reference treatment group (287 days), and a significant reduction of the risk of relapse by 56% at one year (ALVAC IL-2 treatment groups versus reference treatment group) and 65% at two years (ALVAC IL-2 low dose treatment group versus reference treatment group)