A detailed study by an independent research group has confirmed that a class of anemia drugs, including Amgen's ( AMGN) Aranesp and Johnson & Johnson's ( JNJ) Procrit, may increase the risk of death in cancer patients and lower overall survival.

The drugs, formally known as erythropoiesis stimulating agents, or ESAs, prompt the production of hemoglobin in patients undergoing cancer treatments, which can often cause severe anemia. The conclusions reached through the Cochrane Collaboration's detailed meta-analysis reflect results of prior studies, which were incorporated in recent label updates.

Data from clinical trials have shown that higher doses of the drugs may result in worse outcomes, such as higher risk of death and possibly tumor growth, for cancer patients. These safety concerns, and the resulting reimbursement and regulatory issues, have depressed Amgen's anemia drug franchise over the past two years.

The Cochrane Collaboration, an independent, international not-for-profit organization, looked at data on 14,000 cancer patients taking ESAs from previously conducted, randomized, controlled, clinical studies. The data were submitted by Roche, Johnson & Johnson, Amgen and independent investigators.

The organization's most recent analysis differed from those prior as it was done at the "patient level" and not "study level." This means that they reviewed individual data from patients, not just the summary data from the studies.

The meta-analysis found that using ESAs increased the risk of death in the studies and decreased overall survival (although the results were not statistically significant for the population for which ESAs are indicated). This is in line with previous findings from study-level data that is already reflected on the recently updated labels.

"Given that this data has already been incorporated into clinical practice, this is unlikely to change usage materially," wrote Citigroup analyst Yaron Werber, who has a buy/high risk rating for the stock and a $75 price target.

Deutsche Bank analyst Mark Schoenebaum, who has a buy rating and a$73 price target, said that he also expects limited impact on utilization trends, although his team continues to believe Amgen's Aranesp cancer business has not yet reached a bottom.

Amgen is working with the FDA to finalize the risk evaluation and management strategy (REMS) for ESAs to ensure that risks are communicated to physicians and patients.

The prescribing guidelines in the studies used in Cochrane's analyses were not based on the drugs' most recent labels, which are more restrictive.

"Amgen is working diligently with the FDA to initiate prospective studies that address ongoing questions regarding survival when ESAs are used according to the current prescribing information," said Roger Perlmutter, executive vice president of research and development at Amgen.

Complete results of the Cochrane Collaboration's meta-analysis are expected to be presented at a scientific conference later this year. Amgen's shares were down fractionally to $58.74 in recent trading Wednesday.