Toceranib is an anti-cancer drug, developed and registered for use in dogs initially for the treatment of mast cell neoplasia. It is an anti-angiogenic agent (inhibits blood vessel formation) and an anti-proliferative agent (inhibits cell growth and division).[1] It belongs to a class of anti-neoplastic drugs that inhibits the receptor sites of the enzyme tyrosine kinase. There are more than 58 different tyrosine kinase receptors known at present – and when bound, tyrosine kinase enhances such activities as cell growth, metabolism, and adhesion, among other processes. Mutated tyrosine kinases are implicated in unrelated cell growth of tumour cells. The blocking of tyrosine kinase enzyme binding sites with agents such as Toceranib are therefore utilized as effective cancer treatments.
Mast cell neoplasia is a cancer of a type of blood cell normally involved in the body’s response to allergens and inflammation. It is a common skin tumour in dogs, but can also affect other areas of the body, including the spleen, liver, gastrointestinal tract and bone marrow.
Most mast cell tumours in dogs (and some in cats) produce/express a tyrosine kinase growth factor receptor called KTS, and a significant number (up to 50%) have a mutation in the c-kit gene coding for the KIT protein, which results in cells in these mast cell tumours receiving signal to grow, when they normally would not, resulting in uncontrolled tumour growth
Toceranib has demonstrated good efficacy – both as a sole agent, and as part of combination chemotherapy in the treatment of mast cell tumours in dogs in several clinical studies:
It should be noted that response rates to traditional chemotherapy with lomustine (CCNU) are documented at 42% in dogs and 50% in cats.[5],[6]
Can Toceranib Be Used for Other Types of Cancer?
Since toceranib was released, several researchers have investigated the potential use of the drug either alone, or in combination with other treatment modalities – including chemotherapy, radiation therapy, and surgery – in a wide range of cancer types. A summary of some of these studies is included below:
In a randomized study of 126 dogs with osteosarcoma, managed with limb amputation and a 4-dose schedule of carboplatin, dogs were compared in a trial of post-carboplatin cyclophosphamide and piroxicam, or carboplatin/piroxicam with addition of toceranib. Median survival time was not significantly different between the 2 groups. The results of this study showed that addition of toceranib did not improve survival in dogs with osteosarcoma.[7]
In another study of 22 dogs with pulmonary metastasis secondary to osteosarcoma, Toceranib was administered as an adjunct to limb amputation for control of primary disease. No difference in disease-free interval or survival time were noted over untreated historical controls. Overall, the results of this clinical trial do not support the use of Toceranib as single agent therapy for canine metastatic osteosarcoma.[8]
In a prospective study of 43 dogs with haemangiosarcoma, dogs were initially administered doxorubicin for 10 weeks after surgery. Those without evidence of metastasis at that time received toceranib and monitored alongside dogs who had metastatic disease until time of death. Toceranib-treated dogs showed no improvement in median survival time, or disease-free interval over un-treated dogs.[9]
A case series of 3 dogs evaluated the use of toceranib in combination with piroxicam, versus piroxicam combined with carboplatin. All 3 dogs were treated with carboplatin and piroxicam. Dogs 1 and 2 achieved tumour remission. The third dog had a protocol changed from carboplatin/piroxicam to toceranib/piroxicam. Significant tumour reduction occurred in the latter dog, but relapse resulted in patient euthanasia after 195 days. This report suggests Toceranib may be an effective alternative to carboplatin in this tumour type.[10]
A case report of a dog with advanced (stage III) pancreatic insulinoma treated with toceranib and prednisolone was presented, with the patient having stable glycaemic control and survival for over 24 months. Historically, these tumours are associated with a median survival time of 6 months. There may be potential for the use of toceranib in the management of these tumours, based on future studies with larger case numbers.[11]
A prospective study aimed to determine whether addition of toceranib to vinblastine treatment for transitional cell carcinoma was of benefit. Whilst tumour size did reduce over the course of treatment, overall survival time and clinical course was not altered over that of historical controls.[12]
In a study of 5 dogs with the adrenal tumour pheochromocytoma, all 5 dogs in the study that received toceranib as therapy, experienced clinical improvement or stable disease, suggesting toceranib may be of benefit in the management of this tumour.[13]
A ten‐year‐old, female‐entire English springer spaniel with a stromal tumour of the caecum with widespread abdominal metastasis was treated with toceranib phosphate, and had complete response, despite the absence of exon‐8 or exon‐11 c‐kit mutation. There was no clinical evidence of tumour recurrence nine months after diagnosis.[14]
In a prospective study of 18 cats with unresectable injection site sarcomas, toceranib resulted in no measurable positive effect on tumour size or patient disease.[16]
In a study of 85 dogs [17] with various tumours, toceranib was shown to produce either complete, or partial response to the following tumour types:
However, larger trials are considered necessary to elucidate the true nature of the effect of toceranib and any superiority over current treatment protocols, before firm recommendations can be made.
To date, mast cell neoplasia – particularly those with KIT gene mutations – appear to be the most sensitive tumours to toceranib administration. There remains, however, a large body of work to be carried out to definitively determine if toceranib may be of significant use in the management of other tumour types, as much of the work in other tumour types has been carried out with small numbers of patients, which invariably result in data associated with less certainty.
Disclaimer: Every effort has been made to ensure that the information contained in this article is current and correct. No responsibility is assumed by the publisher for loss or injury resulting from any use or operation of methods described herein. Because of rapid advances in medical sciences, independent verification of drug doses and recommendations should be made.
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