Comparison of the efficacy of imatinib mesylate with vinblastine and prednisone in the treatment of canine mast cell tumor: clinical, histological, immunohistochemical and molecular study

Author(s)

Thais Rodrigues Macêdo

• Document type: Doctoral Thesis
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Faculdade de Medicina Veterinária e Zootecnia (FMVZ/SBD)
• Defense date: 2014-08-22

Examining board members

Julia Maria Matera; Thais Andrade Costa Casagrande; Bruno Cogliati; Genilson Fernandes de Queiroz; Angelo João Stopiglia

• Advisor: Julia Maria Matera

Abstract

The objective of this study was to evaluate the efficacy of imatinib mesylate, compared with the usual chemotherapy with vinblastine and prednisone in the treatment of canine mast cell tumor and describe the side effects submitted by medications. Well as analyzing the expression of VEGF (vascular endothelial growth factor), the relationship between the expression of c-kit gene by RT-PCR and immunohistochemical staining of KIT with the presence of mutations in the juxtamembrane and the relationship of this mutation with response to therapy. For both 29 animals with cytological diagnosis of mast cell tumor were included, these animals underwent computed tomography to determine the measured skin formations and then divided into 2 groups. Group 1 was treated with the chemotherapeutic protocol vinblastine and prednisone for 12 weeks and the second group with the imatinib mesylate in a dose of 10 mg / kg every 24 hours for 8 weeks. The assessment of response to treatment was performed with periodic measurements of the formations Caliper and a new computed tomography in the end of treatment to measure the largest tumor diameter and volume. A fragment of skin formations was collected before the initiation of treatment for histological grading, determination of mitotic index, KIT and VEGF staining patterns and the proliferation marker Ki67. Part of the collected material was extracted RNA and DNA and subsequent sequencing of 11 exons of the c-kit gene and determination and expression of its ligand by RT-PCR. The medication toxicity was evaluated according to the standards of VCOG 1.1.A response rate of the VP group was 7.7% and 28.6% MI group, although patients treated with imatinib had a higher chance of response therapy, no difference in response between the two groups was observed. The two protocols were well tolerated, patients in the MI group had a smaller number of side effects. The histological grade, mitotic index, staining patterns KIT, beyond the quantification of Ki-67 were homogeneous in both groups and did not influence the response to treatment. Quantification of VEGF was intensely in patients with partial and total remission. It was no relationship between KIT and quantification of the expression of c-kit gene, which was higher in patients who responded to treatment, but its association with response to therapy cant be determined. Exon11 activating mutations in the c-kit gene were not identified. Treatment with imatinib mesylate is well tolerated by the animals, however this was not superior to standard chemotherapy protocol for the treatment of mast cell tumors; this result may have been influenced by the number of animals included in the study. Mutations in other domains of the KIT receptor and action in ITK receptors as PDGF and VEGF may be related to response to this class of drugs in this study, despite the absence of activating mutations in exon 11 of c-kit gene. (AU)

• FAPESP's process: 10/15093-6 - Comparison of the effectiveness of protocols with imatinib mesylate, and vinblastine with prednisone, prednisone in the treatment of canine mastocytoma-clinical, surgical, histopathological, immunohistochemical and molecular study
• Grantee: Thaís Rodrigues Macedo
• Support Opportunities: Scholarships in Brazil - Doctorate