There's a bidding war brewing for a $10 billion drugmaker

U.S. cancer drug company Medivation is opening its books up to potential buyers.

Medivation entered confidentiality agreements Tuesday, including one with Sanofi that would allow the two companies to engage in deal talks after the French drug company sweetened its $9.3 billion acquisition, Medivation said in a release.

Sanofi's follow-up bid, which was rejected by Medivation, was for $58 per share, with an additional maximum of $3 per share starting in 2022 to account for sales of talazoparib, a drug that's being studied in certain types of breast cancer, as well as other kinds of cancers including cervical, lung, and ovarian.

Medivation has already signed confidentiality agreements to discuss a potential sale with other companies as well, including Pfizer and Celgene, Reuters reported earlier Tuesday.

Medivation shares rose 2.7% after Reuters reported the confidentiality agreement, leaving Medivation with a $10.14 billion market value at the end of Tuesday. The shares rose another 1% in after-hours trading.

Reuters reporting by Michael Flaherty and Greg Roumeliotis.