(Bloomberg) — GlaxoSmithKline Plc will pay U.S. company iTeos Therapeutics Inc. as much as $2.1 billion to develop a potential immune therapy as the British drugmaker rebuilds its pipeline of cancer drugs.

Glaxo and iTeos agreed to develop and commercialize the monoclonal antibody treatment, which is in early-stage trials against advanced solid tumors, they said in a statement Monday. iTeos will receive an upfront payment of $625 million, with additional milestone payments of up to $1.45 billion.

Shares of iTeos soared as much as 77% in trading before U.S. markets opened.

Glaxo has been expanding in the lucrative field since Emma Walmsley took over as chief executive officer in 2017. The company, which had sold its cancer assets to Novartis AG in 2015, now has three oncology drugs on the market, with the therapy area making up about a quarter of its pipeline. The deal comes a week before a key investor day where Glaxo will detail plans to split in two, spinning off its consumer unit into a separate business.

The companies will also test the monoclonal antibody, known as EOS-448, next year in combination with Glaxo’s cancer drug Jemperli, which was approved in the U.S. and Europe in April for recurrent or advanced endometrial cancer. Glaxo and iTeos will share any profits from the tie-up in the U.S.

(Update with iTeos premarket trading in third paragraph)

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