|Systematic (IUPAC) name|
|Trade names||Tykerb, Tyverb|
|Licence data||EMA: , US FDA:|
|Legal status||Prescription Only (S4) (AU) ℞-only (US)|
|Bioavailability||Variable, increased with food|
|Metabolism||Hepatic, mostly CYP3A-mediated (minor 2C19 and 2C8 involvement)|
|Mol. mass||581.058 g/mol|
| (what is this?)
Lapatinib (INN), used in the form of lapatinib ditosylate, (USAN) (Tykerb/Tyverb, GSK) is an orally active drug for breast cancer and other solid tumours. It is a dual tyrosine kinase inhibitor which interrupts the HER2/neu and epidermal growth factor receptor (EGFR) pathways. It is used in combination therapy for HER2-positive breast cancer. It is used for the treatment of patients with advanced or metastatic breast cancer whose tumors overexpress HER2 (ErbB2).
On March 13, 2007, the U.S. Food and Drug Administration (FDA) approved lapatinib in combination therapy for breast cancer patients already using capecitabine (Xeloda, Roche). In January 2010, Tykerb received accelerated approval for the treatment of postmenopausal women with hormone receptor positive metastatic breast cancer that overexpresses the HER2 receptor and for whom hormonal therapy is indicated.
Pharmaceutical company GlaxoSmithKline (GSK) markets the drug under the propriety names Tykerb (mostly US) and Tyverb (mostly Europe). The drug currently has approval for sale and clinical use in the US, Australia, Bahrain, Israel, Kuwait, Venezuela, Brazil, New Zealand, South Korea, Switzerland, Japan, the European Union, Lebanon, India and Pakistan.
The drug lapatinib ditosylate is classified as S/NM (a synthetic compound showing competitive inhibition of the natural product) that is naturally derived or inspired substrate (Gordon M. Cragg, Paul G. Grothaus, and David J. Newman, Impact of Natural Products on Developing New Anti-Cancer Agents, Chem. Rev. 2009, 109, 3012–3043)
Mode of action 
Lapatinib inhibits the tyrosine kinase activity associated with two oncogenes, EGFR (epidermal growth factor receptor) and HER2/neu (Human EGFR type 2). Over expression of HER2/neu can be responsible for certain types of high-risk breast cancers in women. Like Sorafenib, lapatinib is a protein kinase inhibitor shown to decrease tumor-causing breast cancer stem cells.  Lapatinib inhibits receptor signal processes by binding to the ATP-binding pocket of the EGFR/HER2 protein kinase domain, preventing self-phosphorylation and subsequent activation of the signal mechanism (see Receptor tyrosine kinase#Signal transduction).
Clinical application 
Breast cancer 
Lapatinib is used as a treatment for women's breast cancer in treatment naive, ER+/EGFR+/HER2+ breast cancer patients(now often called "triple positive") and in patients who have HER2-positive advanced breast cancer that has progressed after previous treatment with other chemotherapeutic agents, such as anthracycline, taxane-derived drugs, or trastuzumab (Herceptin, Genentech).
A 2006 GSK-supported randomized clinical trial on female breast cancer previously being treated with those agents (anthracycline, a taxane and trastuzumab) demonstrated that administrating lapatinib in combination with capecitabine delayed the time of further cancer growth compared to regimens that use capecitabine alone. The study also reported that risk of disease progression was reduced by 51%, and that the combination therapy was not associated with increases in toxic side effects. The outcome of this study resulted in a somewhat complex and rather specific initial indication for lapatinib—use only in combination with capecitabine for HER2-positive breast cancer in women whose cancer have progressed following previous chemotherapy with anthracycline, taxanes and trastuzumab.
Adverse effects 
Like many small molecule tyrosine kinase inhibitors, lapatinib is regarded as well tolerated. The most common side effects reported are diarrhea, fatigue, nausea and rashes. In ongoing studies the drug has been shown to provoke toxic hepatitis, the toxicity is reversible when the treatment is stopped.
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