Although it's been routinely used since its approval 11 years ago, researchers have only recently discovered that lapatinib (Tyverb in the UK; Tykerb in the US) could be doing more harm than good.
In laboratory tests, researchers from the Francis Crick Institute have shown that the drug helps cancer cells grow much more quickly and spread. The discovery would explain why clinical trials into the drug have come up with poor results, they say. Although the drug has had initial success, it hasn't extended the lives of the patients.
Lapatinib is supposed to curb advanced breast cancers that are caused by an excess of HER2, a protein that signals cancer cells to grow and divide. But instead of interfering with the signalling, the drug seems to help HER2 improve its communications to a partner, known as HER3, which creates a 'signalling pair' that helps the cancer cells spread, the researchers found.
Around 20 per cent of all breast cancers are thought to be caused by an excess of the HER2 (human epidermal growth factor receptor 2) protein.
Lapatinib is routinely used in combination with chemo drugs.