“On average, European veterinary practitioners see between two and three cases of feline fibrosarcoma each year,” reported Pascal Fayard, European marketing manager, citing a survey held among 500 general practitioners in five countries. Speaking at a Merial Conference held in Lisbon on 29 of May, on the eve of the congress of European Society of Veterinary Oncology, he announced the European-wide launch, coming autumn, of a novel immunotherapeutic drug, Oncept IL-2, for the treatment of fibrosarcoma in cats.
Interleukin: stimulating anti-tumour defence
“Interleukin 2 (IL-2) stimulates the growth and activity of T-lymphocytes and natural killer cells, the production of other cytokines like interferon gamma (IFNg) and may improve the tumour-specific immune response,” explained Hervé Poulet, Head of bio development Europe and R&D leader at Merial. “In humans, high-dose systemic IL-2 has been approved for the treatment of metastatic melanoma and renal cell carcinoma”.
However, large doses of systemic IL-2 are associated with several toxic side effects, including the capillary leak syndrome while its clinical efficacy is hampered by the short half-life of IL-2 (a few days). To overcome this, several local IL-2-delivery systems have been studied, including free recombinant IL-2, or IL-2 expressed by DNA plasmids or viral vectors, IL-2 secreting cells and antibody-targeted IL-2. The therapeutic effects of local IL-2 therapy have been demonstrated in several cancers, including equine sarcoids, canine melanoma and non-resectable mast cell tumours.
“For feline fibrosarcoma, we chose a canarypox virus vector (ALVAC®) expressing IL-2: it is very safe as it does not replicate and expresses IL-2 locally. It was found to be an efficacious adjunct treatment to surgery and radiotherapy,” Dr Poulet concluded.
Reducing the risk of relapse by 65%
Results of a monocentric controlled clinical trial were presented by Dominique Jas (Merial R&D) to confirm the efficacy and safety of the product. Seventy-one cats with a first occurrence of feline fibrosarcoma were referred for post-surgical radiotherapy. They were assigned to three treatment groups: controls (surgery + radiotherapy), low-dose IL-2 treatment (surgery + radiotherapy + IL-2) and high-dose IL-2 treatment (surgery + radiotherapy + IL-2). Cats were enrolled 1 month after surgery, which was not necessarily done in referral practices. However, the percentage of cats with dirty surgical margins was comparable in all groups. Treatment (D0, D7, D14, D21, D35, D49) was initiated the day before the start of radiotherapy (D1 and D3). Cats were checked every three months and underwent a CT scan at 3, 6, 12 and 24 months. The high-dose group – to test safety – was monitored for a year, the low-dose group – to test efficacy – for two years.
Local ALVAC IL-2-treated cats showed a significantly longer median time to relapse (>730 days) than in the reference treatment group (287 days). Results also showed a significant reduction of relapse risk compared to the control group after two years (65%). Oncept IL-2 was well tolerated, and the time without relapse was significantly increased with no alteration of quality of life.
“This study showed that the control group, that did not undergo immunotherapy, had poorer results than either treatment group – in spite of the cats receiving a total of thirty injections, Dr Jas confirmed, in answer to the question whether treatment injections were not a risk factors for the development of FISS.
Colleagues from Spain, where there is no radiotherapy available for pets, asked about the possible benefits in cats with surgery alone. “We currently only have a claim for an adjunct therapy to surgery and radiotherapy,” stressed Dr Jas, but she added that this was currently being investigated.
An EU-wide launch this autumn
Oncept IL-2, result of a long-standing collaboration between Merial R&D and leading oncology experts, is the first cancer immunotherapeutic drug approved for veterinary use in Europe.
“We’re very excited and proud to announce the forthcoming launch of a new immunotherapy, a recombinant canarypox virus expressing feline IL-2 at the site of injection, added Catherine Pépin, Merial’s technical manager for companion animals. “The claim is for cats with fibrosarcoma (2-5 cm diameter) without metastasis or lymph node involvement, in order to reduce the risk of relapse and to increase the relapse-free interval.”
“We expect to launch Oncept IL-2 throughout the EU this coming autumn, added Pascal Fayard. He also presented the packaging (“one box contains 6 doses, equal to one course of treatment”) and storage requirements (“in the refrigerator, just like vaccines”). However, the expected retail price was not yet known.
Six sessions, five injections, one treatment
Six sessions with local infiltration (five injections each) in the tumour scar tissue are required. The product’s claim is specific: “reducing the risk of relapse and increasing the time to relapse in cats with fibrosarcoma (2-5 cm diameter) without metastasis or lymph node involvement, in addition to surgery and radiotherapy.”
After reconstitution, five subcutaneous injections (0.2 ml each) are made around the tumour excision site: “one injection at each corner and one injection at the centre of a 5 cm x 5 cm square centered on the middle of the surgical scar.”
A treatment course consists of four sessions at 1-week intervals (day 0, D7, D14, D21) followed by two treatment sessions at 2-week intervals (D35, D49). Treatment is started the day before commencing radiation therapy, preferably within one month after surgical excision.
However, no particular precautions are necessary for administration, as “canarypox recombinants are safe, and feline IL-2 has a very low biological activity”.
First surgical attempt: main prognostic factor
“An association between injections and the development of feline injection-site sarcomas (FISS) was first observed in the late 1980s”, recalled Ana Lara (Royal Veterinary College, UK). Subsequent studies showed a link with a range of injectable drugs triggering local inflammation followed by an abnormal proliferation of fibroblasts and myofibroblasts. “These sarcomas were found to be highly locally infiltrative but with a relatively low (0-24%) metastatic rate.” Although it is a neoplasia that is associated to veterinary practice, there is a potential for prevention and early diagnosis: “we know the risk-population (those receiving injections) and the location (site of injection)”. For these reasons, a benefit-risk analysis is required prior to vaccination while vaccinate in the distal extremities should be considered to maximise the chance of cure in the advent of FISS.
“If FISS is suspected, never perform excisional biopsy – it has a detrimental impact on prognosis,” warned Dr Lara. “In fact, the number one prognostic factor is the first attempt at surgery – which should be aggressive: margins should be 4-5 cm wide and at least 2 fascial layers deep.”
She also recalled the 3-2-1 rule: “biopsy if the lump persists for more than 3 months, if it is larger than 2 cm or if it has appeared within 1 month of injection.” Adding radiotherapy increases the disease-free interval, but not the cure rate – and is not available in all European countries. Chemotherapy is only of interest in cats with unresectable or metastatic tumours.
Speakers at the Merial Conference. From left, Patrick Devauchelle (Animal Oncology Centre, Maisons-Alfort), Dominique Jas (R&D Merial), Catherine Pépin (Technical manager companion animals, Merial), Pascal Fayard (Marketing manager companion animals, Merial), Ana Lara (Royal Veterinary College, London), Hervé Poulet (R&D Merial), Jolle Kirpensteijn (Utrecht University, moderator).