Tykerb (lapatinib) is a first-in-class anticancer drug that this week was approved by the US Food and Drug Administration (FDA) to treat late stage cancers that have spread around the body, in combination with Roche's chemotherapy drug Xeloda (capecitabine).
GSK also filed an approval application for the drug to the European Medicines Agency last year.
"We are finalising some replies to them and we estimate European approval in the second half of this year," said Dr Cristina Oliva, director of oncology at GSK's UK Medicine Development Center.
Breast cancer is the most common cancer to affect women worldwide and each year, more than one million new cases are diagnosed, according to the World Health Organisation.
With a plethora of drugs all competing for a share of the estimated $35bn (€26.5) global cancer market, GSK said it is committed to further clinical trials to investigate the possibility of Tykerb being used to treat early breast cancer and also cancer that has spread to the brain.
The drug is a targeted therapy designed to attack those tumours where a specific protein in found in large quantities.
High levels of human epidermal growth factor receptor 2 (HER2) are found in up to 30 per cent of breast cancers and is associated with aggressive disease and a poor prognosis.
Consequently, several anticancer drugs target HER2.
However, Tykerb is the first drug to target both HER2 and HER1, setting it apart from AstraZenenca's Iressa (gefitinib) - asmall molecule kinase inhibitor that only targets HER1.
The receptors are known to bind together, which then activates the part of the receptor inside the cell - the tyrosine kinase domain.
This leads to the activation of many proteins involved in tumour survival and growth.
Tykerb binds to the tyrosine kinase domain of both HER1 and HER2, preventing these pathways from becoming activated, and so can effectively induce cell suicide.
Genentech has developed the antibody Herceptin (trastuzumab), which also targets HER2, but in a different way.
It binds to the part of the receptor outside the cell, blocking the natural epidermal growth factor and so preventing the cell from dividing and growing.
However, as Herceptin is a large molecule, it cannot easily enter the brain and so it doesn't appear to be useful when the cancer has spread there.
Since, 25 to 48 per cent of all HER2 positive breast cancers spread to the brain, there is an urgent need for more treatments.
GSK hopes that Tykerb could prove to be a useful treatment in this area and Dr Oliva said the company expect to analyse and publish the results from a recently completed clinical trial at a conference later in the year.
If GSK can prove Tykerb is effective in treating brain cancer and early stage breast cancer, it could reach blockbuster status according to industry experts.
Navid Malik, an analyst at Collins Stewart has predicted sales of up to $1bn by 2012.