Biotech Twitter Mailbag: Gilead, Chelsea, Keryx, Onyx, BioSante, Dendreon

BOSTON ( TheStreet) -- A special midweek, all-Twitter version of the Biotech Stock Mailbag:

Please also read part 2 of the Twitter Biotech Mailbag.

@leemambertweets: "More GILD '7977 data due next week @ CROI. Will it be as bad as last data release?"

Gilead Sciences ( GILD) was expected to make a big splash with its hepatitis C drug GS-7977 at next week's Conference on Retroviruses and Opportunistic Infections (CROI). That's no longer true, however, given the poor outcomes for genotype 1 "null responders" already disclosed.

On Feb. 17, Gilead announced results from a cohort in the phase II "Electron" study. Ten hepatitis C genotype 1 patients with a prior "null response" to interferon and ribavirin were retreated with GS-7977 and ribavirin for 12 weeks. Within four weeks of completing treatment, six of eight patients relapsed, meaning the hepatitis C virus, which had been suppressed, came roaring back. Two patients had not relapsed, however they had only reached the two-week post-treatment time point, Gilead said at the time.

Gilead shares are down 16% since Feb. 17 on investors concerns that '7977 may not be as potent a hepatitis C drug as previously expected.

At CROI, Gilead is expected to present an update on these "null" patients treated with '7977 and ribavirin. We have yet to see results for two of the 10 patients and need an update on the two patients who were still relapse free at two weeks post treatment.

If you do the simple math, the best four-week cure rate (SVR4) Gilead can muster from this cohort of patients is 40% i.e. the four remaining patients are all virus free. Likewise, if all the remaining four patients relapse, the four-week cure rate will be 0%.

Obviously, investor expectations are low at this point, but I'd still say Gilead needs to show an SVR4 in at least one or two patients to salvage something positive at CROI and prevent a further slide in its stock price.

CROI's importance is diminished, so the next big hepatitis C data catalyst for Gilead comes later this quarter or early in the second quarter. That's when we'll see results from the '7977+ribavirin combo therapy in two groups of "naïve" hepatitis C patients (those patients new to treatment.)

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