Sanofi CEO Olivier Brandicourt wrote that while Sanofi preferred to acquire Medivation through negotiation, he might have no choice but to go directly to shareholders, who have the ability to act by written consent to replace the board at any time.
"We believe immediate engagement would be in the best interests of your shareholders as it would enable them promptly to realize substantial and certain value, while minimizing the disruption to your organization," Brandicourt wrote in a note to Medivation's board dated earlier this month. "You should know that an acquisition of Medivation is a priority for Sanofi and we are committed to effecting it. ... If the Medivation Board of Directors continues to refuse to engage with us, then we intend to commence a process to remove and replace members of the Board."
Medivation, known for its prostate cancer drug Xtandi, has also reportedly been approached by pharma giant Pfizer.
Goldman Sachs, Morgan Stanley and Medivation declined to comment on the report. Pfizer did not immediately respond to a request for comment.
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— Reporting by CNBC's David Faber. CNBC's Fred Imbert and Reuters contributed to this report.