In the case of Genentech Inc., nothing.

The company declined to seek federal approval for the cheaper drug, Avastin, to treat the wet form of age-related macular degeneration. Nor would it help finance – or cooperate with – a National Eye Institute study comparing the effectiveness and safety of Avastin, a cancer drug, and the more expensive eye drug, Lucentis.

The financial stakes stemming from the study are huge. Medicare officials estimate there could be 50,000 or more additional cases of macular degeneration a year. Treating just one year’s worth of new patients with Lucentis would cost $1.2 billion a year, compared with $60 million if they’re treated with Avastin, Medicare officials said.

Genentech is making no promises that it will act upon the trial’s final results, which are expected in two to three years.

The company has raised concerns that safety issues were not properly addressed. In particular, the trial doesn’t have enough patients to show some of the rare but serious side effects that could occur with use of the cheaper drug, the company contends.

“No matter the outcome, we continue to believe Lucentis is the most appropriate treatment for wet AMD,” said Krysta Pellegrino, a company spokeswoman.

Wet AMD occurs when abnormal blood vessels leak blood and fluid, affecting the part of the eye that sees fine detail.

Many eye doctors believe Avastin works just as well in treating macular degeneration even though it hasn’t been approved for that purpose. It’s not unusual for drugs to be used off-label – treating diseases other than ones the drug was approved for.

Both drugs target a protein that causes blood vessels in the back of the eye to grow, but Lucentis is a much smaller molecule. It was specifically designed – at great expense – to penetrate the retina.

Companies routinely help finance clinical trials, but such trials almost never pit a company’s products against each other.

“It’s a very unusual situation where a company would be trying to compare its own drugs,” said Dr. Frederick Ferris, director of clinical research at the National Eye Institute. “I’m not sure usual situations are all that relevant in this particular case.”

Still, officials pleaded with Genentech to participate in the clinical trial comparing the two drugs. At one point the company considered doing so by providing the medicines in masked, identical vials, according to e-mails obtained by a Senate committee.

“Good news is that the Board supports the proposed studies,” said one e-mail sent in June 2007 from Charlie Johnson, a company vice president, to Dr. Daniel Martin, the chairman of the study who works at the Emory University School of Medicine.

In the end, the board did not support the study. “Our resources would be better spent looking at other diseases where there are no treatments,” said Pellegrino.