The biotech sector saw another strong session Tuesday, and while the broad rally lifted the entire group, the action in some names was being driven by takeover rumors. One of those stocks was Celgene ( CELG), which closed up $2.37, or 7.6%, at $33.47 after speculation made the rounds that Amgen ( AMGN) might have its eye on the company. Another factor helping Celgene's stock was a positive report out of Spain regarding one of the company's cancer drugs. Traders were certainly interested in Celgene, as 8 million shares changed hands, more than five times the normal volume. Amgen, the rumored suitor, ended higher by $1.77, or 2.9%, to $63.65. Another name being discussed in buyout circles was Sepracor ( SEPR), which rose $1.75, or 8.2%, to $23.15. The stock had been as high as $26.25 earlier in the day. As was the case with Celgene, volume was also heavy in Sepracor. The stock spiked at midday and the takeover rumors began. Last week, rumors of consolidation in the sector had some theorizing that Genentech ( DNA) might eventually make a bid for Idec Pharmaceuticals ( IDPH). The two companies have a marketing agreement for the cancer drug Rituxan. Shares of Genentech gained 4.8% to $63.85, and Idec was up 5% to $39.65, after trading as high as $41.22. The Amex Biotech Index finished the day up 5.4%, and the Nasdaq Biotech Index climbed 5.7%. For the time being, analysts didn't seem to be giving a great deal of credence to the speculation that was circulating through the sector, but they did offer some insight as to what might be powering the rumor mill. "Genentech is hitting on all cylinders, and that wouldn't be the best use of their cash," said Jennifer Chao, an analyst with RBC Capital Markets. " But that clearly has been the reason for Idec trading into the $40s. It's a rumor that's surfaced in the past."