Bailey was indeed a very special part of our family and knowing that he received such excellent care from such a wonderful group of people has made this difficult time for us more bearable.
Tyrosine kinases and their inhibitors: Receptor tyrosine kinases (RTKs) are molecules on the surface of cells that bind growth factors which circulate in the blood. Under normal conditions, when the growth factor binds to the receptor, this turns ‘on’ signals to the cell which regulates functions such as cell growth, cell survival, the ability to move and spread, and angiogenesis (development of new blood vessels). In some tumors, this normal process is disrupted due to genetic changes (called mutations) in the receptors or in the growth factors. These genetic changes may cause the receptor to be continuously switched into the ‘on’ position even when the growth factor is not attached to the receptor. If the receptor is continuously ‘on’ this leads to continuous cell growth, leading to tumor growth and spread.
Examples of surface RTKs include Kit, epidermal growth factor receptor (EGFR), vascular endothelial growth factor receptor (VEGFR), and platelet-derived growth factor receptor (PDGFR). Alterations in these RTKs can lead to uncontrolled cell growth and survival and is one of many underlying causes of some cancers. Examples in veterinary medicine include abnormalities in the Kit receptor in mast cell tumors in dogs and cats as well as gastrointestinal stromal tumors in dogs. Abnormal function of the VEGF and PDGF receptors are likely present in a variety of canine and feline cancers including: feline injection site sarcomas, osteosarcoma, anal gland carcinoma, squamous cell carcinoma (canine and feline), hemangiosarcoma, thyroid carcinoma and nasal carcinoma. Currently toceranib phosphate (Palladia; Pfizer Animal Health) is fully licensed and Masitinib (Kinavet, AB-Sciences) is conditionally licensed by the FDA, for treatment in canine mast cell tumors.
These two oral medications are available for use in dogs and several new similar medications are under investigation. Several studies are currently underway evaluating the usefulness of these medications in treating a variety of tumor types including: squamous cell carcinoma, osteosarcoma, nasal carcinoma, thyroid carcinoma, vaccine associated sarcoma, hemangiosarcoma, and anal gland carcinoma. Due to their novel mechanism of action in attacking cancer cells, they can be used alongside our current standard therapies consisting of surgery, radiation therapy and chemotherapy.