GlaxoSmithKline’s breast cancer therapy Tyverb has suffered a setback in Europe after regulators referred the drug back to the Committee for Medicinal Products for Human Use for further consideration, following new data on a potential liver risk.

Tyverb (lapatinib) is the first oral, small molecule, dual targeted therapy that works by getting inside the cancer cell to inhibit two receptors - EGFR and HER2 - responsible for tumour growth, and thereby offers a new weapon for fighting breast cancer. Clinical trials of the drug plus capecitabine have shown its ability to delay the onset of disease progression, and, if approved, the regimen will be indicated for the treatment of patients with advanced or metastatic breast cancer whose tumours overexpress HER2.

Things seemed to be going to plan after the CHMP issued the thumbs up for the drug in December last year, with the full clearance for market entry expected by March 8. But a standard pharmacovigilance review of clinical trial and post-marketing data by GSK in the meantime revealed liver toxicity in four out of a 1,000 patients taking the drug, leading the European Commission to hand back its file to its advisors to assess the risk.

GSK confident
GSK says it now expects Tyverb (lapatinib) to be discussed at the next meeting of the CHMP, which is taking place April 21-24, and stressed that it believes the new findings “do not change the positive benefit-risk profile for Tyverb in the proposed indication”.

If it makes it to market, Tyverb, which is already sold as Tykerb in the US, looks set to face a tough battle for market share with Roche’s Herceptin (trastuzumab), although some analysts expect that it will eventually overtake its rival and generate peak annual sales well in excess of $1 billion. 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.