Phosphorylated KIT as a predictor of outcome in canine mast cell tumours treated with toceranib phosphate or vinblastine

Abstract

Canine cutaneous mast cell tumour (MCT) is the most common malignant skin tumour in dogs and can exhibit variable biologic behaviour. Dysregulated signalling through the receptor tyrosine kinase (RTK) KIT can promote cell proliferation and survival, and assessment of its dysregulation via detection of activating c-kit gene mutations or assessment of KIT protein localization is associated with multiple features of malignancy. The aim of the current study was to use a previously validated immunohistochemical (IHC) assay to directly measure phosphorylated KIT (pKIT) in order to investigate its association with other established prognostic markers, response to therapy, progression free interval (PFI) and overall survival time (OST) in dogs treated medically for measurable MCT. Tumour tissue from 74 dogs enrolled in a prospective study comparing toceranib and vinblastine for MCT treatment were evaluated for pKIT immunoreactivity. pKIT was variably expressed, with some degree of positivity observed in 49/74 cases (66%). pKIT immunoreactivity was significantly associated with aberrant KIT localization, high mitotic index and high histologic grade.On univariate analysis, pKIT immunoreactivity predicted shorter PFI and OST in the entire patient population as well as shorter PFI in the toceranib treated group, and was the sole predictive factor for OST upon multivariate analysis, while mitotic index was the sole independent predictive factor for PFI. These results demonstrate that IHC detection of pKIT correlates with several features of aggressive behaviour, and may confer information that is complementary to other prognostic factors. However, the role of pKIT in predicting outcome needs to be studied further before recommendations can be made for its routine use. K E Y W O R D Scancer, chemotherapy, dog, kinase, mutation

Horizons in Veterinary Precision Oncology: Fundamentals of Cancer Genomics and Applications of Liquid Biopsy for the Detection, Characterization, and Management of Cancer in Dogs

“…In the EU, the European Medicines Agency (EMA) has approved toceranib, tigilanol tiglate and mastinib mesylate (Masivet R ) (237). Of these approved or conditionally approved drugs, only toceranib (a multi-kinase inhibitor that inhibits c-kit, PDGFR, and VEGFR2), and mastinib (a c-kit inhibitor) can be used as a targeted drugs linked to specific genomic features of a tumor, as improvements in tumor response (43, 238) and outcome (239) have been demonstrated for tumors with an activating kit mutation; however, many targeted drugs used to treat human disease are currently used off-label in dogs (236,240). Many compounds developed (and FDA-approved) for use in humans underwent preclinical safety testing in dogs; significant safety and dosing data are thus available to help inform the treatment of canine cancer patients with these agents (241).…”

Histological classification and expression of markers of canine mast cell tumors

“…Even without observing the animals after tumor excision, the results obtained in the Grade 1 group suggest that canine MCT should not be considered benign in any histological grade, due to its variable biological behavior and prognosis. The biological behavior of canine MCTs [ 43 ] ranges from solitary benign nodules to systemic metastatic tumors, which hinders the accuracy of prognosis and choice of treatment [ 17 ]. In addition, our study did not evaluate the presence of metastases, which would be relevant, as dogs with distant metastases had significantly shorter survival than those with regional lymph node metastases [ 44 ], which are also a negative prognostic indicator, regardless of histological grade [ 45 , 46 ].…”

In situ c‐KIT mRNA quantification of canine cutaneous mast cell tumours and its relationship to prognostic factors

“…Although exon 11 mutations are the most common mutations in cutaneous MCTs, mutations at other sites were not assessed in this study and should be considered in future studies. Additionally, recent studies have shown that measuring the KIT phosphorylation status by IHC is an additional tool to determine the c ‐KIT activation status 41,42 . Further research is needed to determine the relationship between c ‐KIT mRNA expression and KIT phosphorylation.…”