The success rate in bringing new medicines to market in recent years is only about half of what it had been previously, but biotech drugs are twice as likely to gain U.S. approval than more traditional chemical drugs, according to a new study released on Monday.

And while oncology has been one of the hottest and most active therapeutic areas for drug development, drugmakers may want to take note of a finding that new cancer drugs have proven far more difficult to gain approval than medicines for infectious and autoimmune diseases.

Drugmakers have been complaining about the difficulty of bringing new products to market in a regulatory climate that has become increasingly unpredictable and more likely to err on the side of safety in deciding risk/benefit ratios of experimental medicines.

Data from this new study appears to bear that out.

"It ain't getting any easier to develop new therapies." said Alan Eisenberg, head of emerging companies and business development for the biotech trade group Biotechnology Industry Organization (BIO), putting the findings succinctly.

"Knowing more about the magnitude of risk can lead to smarter drug development as well as smarter investing," he said.

The study, covering 2004 through 2010, found the overall success rate for drugs moving from early stage Phase I clinical trials to FDA approval is about one in 10, down from one in five to one in six seen in reports involving earlier years.

The study, conducted by BIO and BioMedTracker, which collects data on drugs in development, reviewed more than 4,000 drugs from companies large and small and both publicly traded and private. It was released in conjunction with the annual BioCEO and Investor conference in New York.

Adding weight to the desire by major pharmaceutical companies to become increasingly involved in biotechnology was a finding that biologics had a 15 percent chance of going from Phase I through to FDA approval, compared with a 7 percent success rate for traditional small molecule chemical drugs.

When broken down by therapeutic categories, the highest overall success rate from Phase 1 through likelihood of approval was infectious diseases, such as hepatitis and HIV drugs, at 12 percent, followed by endocrine system drugs, featuring diabetes treatments, at 10.4 percent, and autoimmune diseases, such as rheumatoid arthritis, at 9.4 percent, the study found.

John Craighead, BIO's managing director for investor relations, said clinical trial goals and the approval pathways for infectious diseases and diabetes drugs are clear and very well-established.

"The Phase II results are very predictive of the Phase III outcomes and very predictive of approval," he said.

"The overall success rate in oncology was the lowest of the therapeutic areas that we looked at," he said, noting that cancer studies vary dramatically in design and extending survival sets a high bar for approval.

The cancer drug success rate was a mere 4.7 percent, with cardiovascular drugs second-worst at 5.7 percent, as regulators are increasingly demanding proof that heart drugs reduce heart attacks and strokes rather than just lower a risk factor, such as cholesterol levels.