GlaxoSmithKline has laid down a marker ahead of the American Society of Clinical Oncology (ASCO) annual meeting next month, staking its claim as a major new force in cancer treatment.

The company will present data on a raft of new drugs, including Tykerb (lapatinib ditosylate), a potential competitor to Roche’s big-selling Herceptin (trastuzumab) for breast cancer, which brought in revenues of $1.8 billion last year, a rise of 50% on the previous year.

Tykerb is an orally-active tyrosine kinase inhibitor, inhibiting both the HER-2 receptor (Herceptin’s target) and the epidermal growth factor receptor, and GSK hopes it can quickly stake a claim to treating patients who do not respond to Roche’s intravenously-administered drug. Thereafter, the company plans to progressively expand Tykerb’s indications into the first-line and adjuvant settings.

Cancer accounts for a relatively small proportion of GSK’s sales at present, accounting for a little under 9% of its first quarter sales and driven by lung cancer drug Hycamtin (topotecan) and Zofran for nausea and vomiting associated with chemotherapy.

But this looks set to change if Tykerb and other drugs in cancer pipeline reach the market. Tykerb has been predicted to have multibillion dollar sales potential, and is scheduled to reach the market next year, along with eltrombopag for thrombocytopenia cervical cancer vaccine Cervarix. Meanwhile, another potential big seller, the nasea and vomiting treatment casopitant, is due to reach the market in 2008.

At ASCO, the company will present late-breaking data on Tykerb in Herceptin-resistant breast cancer, as well as Phase II data in patients with brain metastases in patients with HER-2-positive breast cancer, a group which Herceptin cannot treat effectively, as well as relapsed/refractory inflammatory breast cancer and renal cell carcinoma. It will also present data that should show that Tykerb has a low tendency to cause cardiac toxicity.

Meanwhile, another much-anticipated presentation will be on GSK’s MAGE-3 antigen specific cancer immunotherapeutic as adjuvant therapy in non-small cell lung cancer, while a long-term prospect is angiogenesis inhibitor pazopanib, for which Phase I data in combination with Tykerb will be shown.