By Joshua Jamerson 

Medivation Inc. on Friday said it rejected Sanofi SA's $9.3 billion takeover offer, claiming that the French drugmaker's proposal "undervalues" the cancer-treatment company.

The move by Medivation comes one day after Sanofi said it made an unsolicited offer, which was its latest effort to expand its cancer-treatment business.

Medivation said its board had unanimously rejected the Sanofi's offer and that the proposal would deny its shareholders of the value in its late-stage pipeline, as well as its flagship oncology drug, Xtandi.

Sanofi responded Friday by saying it remained "committed" to the transaction and looked forward to "engaging directly with Medivation shareholders."

Sanofi's offer of $52.50 a share was a 50% premium on Medivation's average share price for the two months before takeover speculation emerged, though lower than Medivation's current share price, which was buoyed by takeover speculation.

Medivation's shares rose 0.1% to $56.20 in early trading in New York, while Sanofi shares fell 3% in Paris trading.

Write to Joshua Jamerson at joshua.jamerson@wsj.com

(END) Dow Jones Newswires

April 29, 2016 10:00 ET (14:00 GMT)