German pharmaceutical group Bayer is preparing a bid to acquire Algeta, its partner for its prostate cancer treatment Xofigo, a German newspaper reported on Tuesday.

The Frankfurter Rundschau, citing internal documents it obtained, said Bayer would offer 306 Norwegian crowns ($49.9) per share for a Norwegian stock-exchange listed company, referred to in the documents as "Aviator". The newspaper said it believed this company to be Algeta.

This would be a near 16 percent premium to Algeta's closing price on Monday of 264.60 crowns and would value the Norwegian company at 13.4 billion crowns, or roughly 1.63 billion euros.

"I don't know anything about that," Algeta chief technology officer Thomas Ramdahl told Reuters, when asked about a 306-crown-per-share bid. "I don't have any comments on the issue," he said.

A spokesman for Bayer declined to comment.

Algeta and Bayer Healthcare are co-promoting Xofigo in the United States. Xofigo, also called Radium-223 dichloride, is designed to target bone metastases from prostate cancer that cannot be treated by standard hormone therapy.

The drug, which according to Bayer could become a "blockbuster" product with annual sales of least 1 billion euros, has some properties of calcium. That makes it cling to cancerous bone cells and then destroy them via alpha rays, which is more targeted than the shotgun approach of conventional radiotherapy.