Reliance on China health sector raises searching questions for Baidu

* Student dies after cancer treatment found on Baidu search

* Baidu, hospital under investigation by regulators

* Baidu gets 20-30% of search revenue from healthcare -analysts

* Baidu search revenues in 2015 were $8.6 bln, 84 pct of total

* Baidu at risk of curbs on advertising, public loss of faith

By Paul Carsten

BEIJING, May 7 (Reuters) - The death of a student following experimental cancer treatment he found through China's biggest search engine, Baidu Inc, has exposed the faultlines in the company's business model, which relies heavily on income from the country's lightly regulated health sector.

Before his death, student Wei Zexi, 21, criticised the military-run hospital that provided the failed treatment for misleading claims about its effectiveness and accused Baidu, which controls 80 percent of the Chinese search market, of promoting false medical information.

This week the health ministry began an investigation into the hospital, while the internet regulator began an investigation into Baidu.

The regulators have not said what, if any, offences or regulations might have been broken and did not respond to requests for comment.

Analysts at Daiwa said regulators could be checking for compliance with China's Advertisements Law, which says medical sector advertising should not contain assertions about effectiveness.

Baidu said it was also conducting an investigation and would fully cooperate with the regulator.

It is not clear that conventional treatment - typically surgery to remove the tumour - would have cured the rare synovial sarcoma that Wei suffered from.

Reuters has not been able to reach the hospital for comment.

Baidu has come in for fierce online criticism for how it handles adverts within its search results, especially from an industry as sensitive as healthcare, which analysts at Nomura and Daiwa say provides 20 to 30 percent of its search revenues.

In 2015 search revenues were 55.7 billion yuan ($8.6 billion), or 84 percent of Baidu's total sales.

"Whatever page you're looking at on Baidu is a mess of adverts," said username FreedLiu on China's Weibo microblog, discussing Wei. "They're profiting from loads of people who don't know Baidu auctions (its search results)."

Baidu said it applied particular vigilance to healthcare customers, with screening for misleading adverts and a verification programme with additional scrutiny for medical advertisers.

"Over the years, we have proactively cleaned up the customer base," a company spokeswoman said by email.

It is not the first time the company has fallen foul of regulators and public opinion for its handling of healthcare ads and blogs, though it has not suffered substantive sanctions.