AstraZeneca said on Wednesday its China president Leon Wang had been detained by Chinese authorities and, although it did not know the reason, it did not believe it was linked to a large health insurance fraud case involving the company.

Two current and two former senior executives at AstraZeneca Plc are under investigation in China in an ongoing probe into alleged breaches of laws around drug importations and data privacy, the company said.

BMO Capital Markets analyst Etzer Darout in a note to investors said the insurance fraud probe represents a “headline risk” to AstraZeneca, but contends that the share selloff is “overdone” and likely a knee-jerk reaction by investors.

The company believes Chinese authorities are probing allegations that two current and two former employees had illegally imported cancer drugs.

AstraZeneca Plc shares plunged in London, erasing about £14 billion ($18 billion) of market value, amid escalating concerns over a Chinese probe into the UK drugmaker.