Gilead Sciences (GILD) took another step forward with its hepatitis C drug program Tuesday, showing a strong cure rate for hard-to-treat patients in a late-stage study. The data met Wall Street expectations and is significant because it is the first of several trials in the final round -- or so-called Phase III stage -- of study necessary to win U.S. approval.

The company is expected to announce three more Phase III trial results in the first quarter of 2013 and will likely file for Food and Drug Administration approval for its drug, Sofosbuvir, by the middle of next year. Based on Tuesday’s results and earlier study data, analysts predict that Gilead’s drug is a winner. A number of investors are betting that way as well. Gilead shares are up more than 90% in the past 12 months, trading at $75.25 midday Tuesday.

The latest data showed that 78% of study patients with chronic hepatitis C remained free of the virus 12 weeks after completing a regimen of Sofosbuvir and the older drug Ribavirin. The study included patients who cannot tolerate or who are ineligible or unwilling to receive the injected drug Interferon. Despite the approval last year of breakthrough drugs made by Vertex Pharmaceuticals (VRTX) and Merck (MRK), the standard of care for the liver-destroying virus still requires Interferon, which carries nasty, flu-like side effects. The goal of Gilead, Abbott Laboratories (ABT), and others is to develop an all-oral regimen that cuts out the need for Interferon. The Gilead drug appears to do that effectively.

"Achieving a sustained virologic response in three quarters of patients is an impressive result for a Sofosbuvir-based, all-oral treatment in a group of individuals for which no suitable alternative therapy exists," says Gilead Chief Scientific Officer Norbert Bischofberger in a statement.

The just-announced results are for a study that only included patients with a certain genetic makeup -- genotype 2 or 3, which represents about one third of all hepatitis C patients, according to ISI Group analyst Mark Schoenebaum.

Gilead is also testing its drug for the more common genotype 1 patient and it is also studying the use of its drug without Ribavirin. The FDA application Gilead is expected to file next year would be just the first as the company will seek additional indications for the treatment. What’s important is that an all-oral treatment gives Gilead (or a rival company) the opportunity to transform the market for these type of treatments.

"The results seen to date with Sofosbuvir (with or without other agents) look promising, and we continue to believe this agent could be an effective backbone therapy for the treatment of hepatitis C," William Blair analyst John Sonnier says.

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