Amgen's ( AMGN) anemia-drug franchise was dealt more foreboding news Thursday when the Food and Drug Administration stiffened its safety warning to health care professionals to include flag-raising mortality rates in recent studies.

The agency cautioned that the so-called Prepare breast cancer study as well as a study in cervical cancer by the National Cancer Institute Gynecologic Oncology Group showed greater death rates and tumor progression in patients who received erythropoiesis-stimulating agents (ESAs), such as Amgen's former blockbuster drugs Epogen and Aranesp and Johnson & Johnson's ( JNJ) Procrit, which are used for chemotherapy-induced anemia and anemia associated with chronic renal failure.

"This new information further underscores the safety concerns regarding the use of ESAs in patients with cancer addressed in previous communications," the agency noted.

Amgen's stock hit a new 52-week low on Thursday, dipping down to $45.25 and closing at $45.69. It has traded as high as $76.95 in the last year but has taken a beating with the decline of its anemia-drug franchise.

On Wednesday, Lazard analyst Joel Sendek upgraded the stock to hold from sell, noting that he believed the stock was fairly valued as it had sank to his $46 price target. "...We now believe the risks to the ESA franchise and competitive threats to Enbrel, denosumab, and the NEUPO franchises are priced in," he wrote in a research note.

Earlier in December, Amgen notified the FDA that the cervical cancer study stopped enrolling patients because the arm with ESAs was showing a higher rate of potentially life-threatening blood clots. The Prepare study has sparked similar safety concerns in breast cancer patients. The study aimed to show a cancer-fighting benefit of adding Amgen's Aranesp to standard cancer therapy.

In addition to increased mortality rates in the ESA-treated arm, an interim analysis showed Aranesp had no significant impact on how tumors responded to chemotherapy at the time of surgery.

The FDA said Thursday that it's reviewing information on the ESAs and will take additional actions as appropriate. In early 2008, an advisory committee will meet to re-evaluate the risk and benefit balance of the drugs. "In the interim, healthcare professionals should consider the risks of tumor progression and decreased survival observed when ESAs are used as supportive care in patients with cancer," the agency noted.

Amgen's shares were down 91 cents, or 1.96%, to 45.69 in recent after-hours trading.

More from Stocks

Week Ahead: Trade Fears and Stress Tests Signal More Volatility To Come

Week Ahead: Trade Fears and Stress Tests Signal More Volatility To Come

3 Great Stock Market Sectors Millennials Should Invest In

3 Great Stock Market Sectors Millennials Should Invest In

Why Millennials Are Ditching Stocks for ETFs

Why Millennials Are Ditching Stocks for ETFs

Trump's 'Space Force' Could Launch a $1 Trillion Industry, Morgan Stanley Says

Trump's 'Space Force' Could Launch a $1 Trillion Industry, Morgan Stanley Says

Abiomed Stock Should Rise Some 12% From Here, Piper Jaffray Analyst Says

Abiomed Stock Should Rise Some 12% From Here, Piper Jaffray Analyst Says