Shares of Cubist Pharmaceuticals ( CBST) were among the best-performing health-related stocks Thursday, rising 5% after the company posted a third-quarter loss that was smaller than expected. The company's loss narrowed to $4.5 million, or 8 cents a share, from $17.7 million, or 14 cents a share, a year earlier. Sales surged to $31.8 million from $19.4 million on growth in sales of Cubicin, a bactericidal antibiotic. Analysts polled by Thomson First Call were expecting a loss of 15 cents a share and sales of $32.5 million. Shares recently traded up 98 cents to $19.03. MedImmune ( MEDI) shares rose 3% after the company posted a huge jump in third-quarter sales on strength of the respiratory treatment Synagis. The company reported a loss of $64.1 million, or 26 cents a share, on sales of $153.6 million. Excluding items, the company had a loss of $60.8 million, or 25 cents a share. Analysts were expecting a loss of 22 cents a share, before items, on sales of $107.5 million. A year ago, the company reported an adjusted loss of $55 million, or 22 cents a share, on sales of $92.7 million. MedImmune backed its fourth-quarter adjusted earnings guidance of 24 cents to 30 cents a share, which is above analysts' mean estimate of 22 cents a share. Shares gained $1.15 to $34.50. Shares of Quest Diagnostics ( DGX) fell 1% after the company posted third-quarter earnings that matched expectations, but cut its full-year guidance. The medical testing company earned $135.2 million, or 66 cents a share. Quest said the Gulf Coast hurricanes and an investment writedown cut per-share earnings by 5 cents during the quarter. Without the items, the company would have earned 71 cents a share, matching analysts' forecast. Quest's sales of $1.37 billion came in slightly ahead of analysts' projection of $1.36 billion. A year earlier, the company earned $130.1 million, or 62 cents a share, on sales of $1.29 billion.