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.

"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.