LONDON – Roche Holding AG is likely to sweeten its offer for Genentech Inc to between $102 and $105 a share, from $89 at present, according to a top fund manager and shareholder in the U.S. biotech group.

Sam Islay, founder and managing partner of OrbiMed Capital LLC, reckons Roche started low when it announced its surprise move last week to give headroom for a higher – but still viable – offer later on.

“I reckon they'll bump to somewhere between $102 and $105; that is my projection,” Islay said in an interview during a visit to London.

“Whether a bump to $102 or $105 will actually swing it, that I don't know.”

Most analysts view an eventual deal as likely, although many say Roche will need to raise its $43.7 billion offer for the 44 percent of Genentech stock that it does not already own.

Islay said Roche would have to win over minority shareholders, given the bright future for the California-based leader in cancer drugs as a stand-alone business.

But he is not too concerned about the the potential culture clash involved in bringing Genentech inside the giant Swiss healthcare group, which some commentators have said could lead to a damaging flight of top Genentech talent.

“Overall, I would think Roche could do a decent job at owning it all and preserving the culture,” he said.

He believes Roche Chairman Franz Humer and CEO Severin Schwann are playing a shrewd hand.

“If you were Humer and Schwann, how would you go about it? Would you go in at $105 and stand firm? Or woulisted Finsbury Worldwide Pharmaceutical Trust Plc.

(Editing by David Cowell)