Flexion  (FLXN) - Get Report shares were up 38% to $27.20 on Thursday following reports that Sanofi  (SNY) - Get Report was nearing a $1 billion plus bid to purchase the arthritis-focused biotech company. 

Flexion's board has voted to accept Sanofi's bid, according to a report by Fierce Pharma. That same report noted that the talks of a deal may not come to fruition. And many on Twitter were skeptical of the report, noting that it could simply be a rumor. Sanofi shares were unmoved on the report. 

Flexion officials said by phone that it's company policy to not comment on market rumor or speculation.

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"Our strategy is to advance Flexion independently," said spokesman Scott Young by phone Thursday. "We are looking forward to our Oct. 6 PDUFA date."

The company announced Feb. 17 that it had its new drug application (NDA) for its lead candidate, Zilretta, a drug for osteoarthritis, accepted by the Food and Drug Administration. The PDUFA date is a deadline for the FDA to approve a new drug.

Sanofi officials could not be reached for comment Thursday.