GlaxoSmithKline is celebrating after US regulators, as expected, gave the green light to the company’s new oncology agent Tykerb.

The US Food and Drug Administration has granted marketing approval for Tykerb (lapatinib) in combination with Roche’s chemotherapy agent Xeloda (capecitabine), for the treatment of patients with advanced or metastatic breast cancer whose tumours overexpress HER2 and who have received other therapies including Herceptin (trastuzumab). Roche and Genentech market the latter, which is the first-line treatment for HER2 positive advanced breast cancer. The gene makes the cancer more aggressive.

The approval is based on a Phase III trial of 399 patients which showed that the median time to disease progression was 27.1 weeks on the combination of Tykerb and Xeloda versus 18.6 weeks on capecitabine alone in women with advanced or metastatic HER2 (ErbB2) positive breast cancer whose disease had progressed following treatment with Herceptin and other therapies. GSK noted that the FDA’s positive decision “reflects more than 16 years of research, including more than 60 clinical trials and investigator-initiated collaborative research studies.”

Tykerb has been the jewel in GSK’s R&D crown, having reported a steady stream of data from the clinic and analysts are confident it can reach blockbuster status. The drug is also being studied in a number of other indications and GSK recently announced the start of the first late-stage trial of Tykerb in squamous cell carcinoma of the head and neck. Studies are also going in brain and kidney cancer.

The potential of Tykerb is such that analysts have suggested that it may eventually overtake Herceptin, which generated 3.93 billion Swiss francs (around $3.23 billion) in sales last year. This view is due in part to the fact that GSK’s drug has the advantage of being orally-active while Herceptin is dosed by injection. Both block the HER-2 receptor, but Tykerb also has activity against the epidermal growth factor receptor.

Also, GSK has suggested that Tykerb may lack the potential for cardiotoxicity seen with Herceptin, and because it is a small molecule can cross into the central nervous system to tackle brain metastases, something that Herceptin - an antibody - cannot do.