Cubist Pharmaceuticals ( CBST) shares sank Thursday after the stock was downgraded by research firm JMP Securities to market outperform from buy, citing a lack of near-term catalysts.

Biotech analyst Adam Cutler says the stock is cheap, however, and that "sales trends have been healthy, and there should be plenty of growth left." Cutler lowered his price target on the stock to $24 from $28. Shares fell 3.2% to $17.62.

Shares of Quest Diagnostics ( DGX) lost 1.2% to $50.46 after the lab specialist guided lower for 2007.

The diagnostic test outfit earned $151 million, or 77 cents a share, in the fourth quarter, above analysts' estimates of 74 cents a share. Revenue grew 8.5% to $1.55 billion. Analysts expected revenue of $1.57 billion. For 2007, the company expects earnings of between $2.70 and $3 a share on $6 billion to $6.2 billion in revenue. Analysts were expecting earnings of $3.21 a share on sales of $6.4 billion for the year.

St. Jude Medical's ( STJ) shares rose 4.3% to $41.37 Thursday after the medical device maker reported an increase in fourth-quarter earnings and issued guidance for growth in 2007.

The company earned $155 million, or 42 cents a share, including a retroactive benefit of approximately 3 cents a share related to a research and development tax credit for the first nine months of 2006. Analysts were expecting the company to earn 39 cents a share. Sales were $864 million, up more than 9% from the fourth quarter of 2005 and exceeding analysts' estimates of $852.35 million.

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