Significance of Tyrosine Kinase Inhibitors in the Treatment of Metastatic Breast Cancer.

Preclinical and clinical trials suggest that tyrosine kinase inhibitors (TKI) could supplement current therapies in metastatic breast cancer (MBC). HER-2 inhibition is still a main focus. Numerous agents targeting the epidermal growth factor receptors EGFR and HER-2 are currently tested after previous trastuzumab treatment. Lapatinib targets HER-2 and EGFR. As monotherapy, clinical activity was low. Combined with cytotoxic agents, lapatinib showed good activity (overall response rate (ORR) 24-27%) and moderate toxicity. Neratinib, a pan-ErbB TKI, showed an ORR of 26%. Neratinib combined with trastzumab was well tolerated and active (ORR = 27%). After bevacizumab's proof-of-concept studies, anti-angiogenesis remains of importance. Sunitinib inhibits the vascular endothelial growth factor receptor (VEGFR), the platelet-derived growth factor receptor (PDGFR), c-kit and the colony-stimulating factor 1 (CSF-1) receptor. Monotherapy is tolerated and moderately active in MBC. Combination trials are ongoing. Toxicities of docetaxel ± sunitinib were manageable (ORR 72.2%). Pazopanib targets VEGFR, PDGFR and c-kit. Pazopanib ± lapatinib was superior in combination (progression-free survival (PFS) = 27% vs. 19%). Axitinib has similar targets. Combined with docetaxel, it was superior compared to placebo (ORR 40% vs. 23%), with manageable toxicity. Imatinib inhibits PDGFR and c-kit. As monotherapy, it showed no clinical activity. Combination trials with chemotherapy are ongoing.