Buyout fever launched biotech stocks higher Thursday, pushing earnings to the back burner for a day.

The Amex biotechnology index rallied 4.1% to 864.14. The rally got started early when

Bristol-Myers Squibb

(BMY) - Get Report

announced a

$60-a-share bid

to buy

ImClone

(IMCL)

, valuing the biotech company at $5.2 billion.

Shares of ImClone, a component of the Nasdaq biotech index, soared $17.49, or 37.7%, to $63.93 while Bristol shares gave up 39 cents, or 1.8%, to $63.93.

The buyout enthusiasm spilled over to other stocks as investors pondered the possibility other such

Big Pharma-biotech mergers

.

Amylin

( AMLN) and

Onyx

(ONXX)

gained 14.8% and 10%, respectively.

In clinical and regulatory news,

Genmab

and

GlaxoSmithKline

(GSK) - Get Report

reported positive preliminary results from a late-stage trial on ofatumumab for patients with chronic lymphocytic leukaemia, or CLL, and said they plan to file for U.S. and European regulatory approval by the end of the year.

If approved, the drug could compete with

Genentech

( DNA) and

Biogen Idec's

(BIIB) - Get Report

Rituxan.

Glaxo shares ended essentially flat, while Biogen Idec fell $1.51, or 2%, to $69.76 and Genentech edged up 25 cents, or 0.3%, to $95.25.

A legal and regulatory item, generic-drug maker

Barr Pharmaceuticals

( BRL) is striking again. The company said it is challenging a patent held by Belgian drug maker

UCB Inc.

for 5-mg tablets of hay fever treatment Xyzal. UCB filed a patent infringement lawsuit against Barr on Wednesday. The drug was developed by

Sepracor

( SEPR) and licensed to UCB.

Sanofi-Aventis

(SNY) - Get Report

markets it in the U.S.

Barr's shares traded up 68 cents, or 1%, to $65.98.

In other regulatory news, shares of

Cadence

(CADX)

climbed $3.87, or 60.3%, to $10.29 after the company said the Food and Drug Administration will not require any additional trials for its new-drug application (NDA) for Acetavance, an intravenous formulation of acetaminophen. Pending the completion of three ongoing trials, it anticipates filing the NDA in the second quarter of 2009 for approval to treat acute pain and fever in adults and children.

And, of course, earnings. British drugmaker

AstraZeneca

(AZN) - Get Report

reported net profit of $1.62 billion in the recent quarter, up from $1.43 billion a year prior, on revenue that rose 9% to $7.96 billion. The company upped its 2008 core earnings per share guidance by 15 cents to a range of $4.60 to $4.90. Shares rose 3.8% to $48.55.

On the falling side, medical technology company

Hologic

(HOLX) - Get Report

missed adjusted profit estimates by 4 cents a share and reined in full-year guidance. Jefferies analyst Arthur Henderson downgraded the stock to hold from buy and cut his price target to $24 from $28. Shares were down $4.38, or 19.2%, at $18.47.