LONDON – GSK Chief Executive Emma Walmsley, the first woman to lead a major pharmaceutical company, will step down Dec. 31 after more than eight years at the head of the London-based drugmaker.

Walmsley, 56, will be replaced by Luke Miels, currently GSK’s chief commercial officer, the company said in a statement released on Monday.

While GSK achieved a number of strategic successes under Walmsley, including the spinoff of the consumer health care business Haleon, it has disappointed investors. GSK’s shares rose 3.3% to 1534.50 pence in early trading, making it the biggest gainer on the London Stock Exchange.

GSK’s shares fell 11% between April 1, 2017, when Walmsley became CEO, and last Friday.

“Despite the progress, the share price performance has been lackluster,” Derren Nathan, head of equity research at U.K.-based Hargreaves Lansdown,” said in a note to investors.

“Although her record of delivering on financial guidance has been strong, the company’s growth rates remain stuck in single-digit territory.”