Baidu said in a statement that it will fully enforce the regulators' demands by examining all medical-related promotions. It will also place clear disclaimers on advertisements so that online searchers can tell them from natural search results.

The company said that by Monday it had reviewed the qualifications of all related medical institutes and had stopped listing 2,518 of them. A total of 126 million promotion entries had also been removed.

A search by China Daily's for "infertility" — a popular content for medical advertising on Baidu — found on Monday night only one promotion, separated from the listings on the page, and clearly marked as an advertisement. The same search three days ago turned up an entire page of promotions.

Analysts said that changing the rules on how to conduct paid listing business will hurt Baidu's profitability in the near term, as medical-related advertisements account for about 30 percent of the company's revenue.

Tian Hou, founder of TH Capital in Beijing, said the tricky part is how to search results by reputation.

"A high reputation for medical treatment may still hurt patients," Tian said. Medical-related paid promotions are a problem for Baidu, and if they are not completely cut out, this will rekindle concerns for the company's business, Tian added.

Baidu did not immediately respond to requests for comment on how to rank paid listings by reputation.

On Monday, the central government and military health authorities also announced the investigation result into the hospital involved.

It was ordered to stop all commercial cooperation with private companies and check whether it has conducted any other clinical treatment that has not been approved.

Doctors involved will have their licenses revoked. Anyone suspected of violating the law will be transferred to judicial authorities, according to the investigation result.

The National Health and Family Planning Commission has said that immunotherapy to treat cancer is still at the scientific research stage and should not be used for clinical treatment. The hospital declined to comment on Monday.

Contact the writers at caoyin@chinadaily.com.cn