With the SPDR S&P Biotech Index up 43% over the trailing-12-month period, it's evident that investment dollars are willingly flowing into the biotech sector. Keeping that in mind, let's have a look at some of the rulings, studies, and companies that made waves in the sector last week.

If there was a theme this week, it was that the majority of the big moves went to small-cap biotechs. As is tradition, let's look at some of the most encouraging stories of the week to start.

Ending on a positive note
Perhaps nothing was more of a confidence booster for Zogenix (NASDAQ:ZGNX) shareholders than the announcement on Friday that the Food and Drug Administration had approved Zohydro ER for the treatment of chronic severe pain management. Zohydro ER is an alternative to Vicodin in that it doesn't contain acetaminophen, so it could serve a decent-sized niche of chronic pain suffers. The real surprise was the approval itself given that the FDA's advisory panel voted 11-2 against recommending Zohydro ER for approval due to concerns about the potential for abuse of the drug. The FDA, in a rare move, went against this recommendation, but did require Zogenix to complete a post-approval addiction study. This approval, assuming a successful drug launch, could go a long way to reducing Zogenix's current cash burn rate. Shares gained 32% on the week.

Despite ending the week about 2% lower, Immunomedics (NASDAQ:IMMU) also delivered a shot of good news into the arms of shareholders on Wednesday when it announced positive early-stage clinical results for 90-Y clivatuzumab tetraxan in combination with a low dose of Eli Lilly's Gemzar as a treatment for advanced pancreatic cancer. According to the press release, patients that were given multiple rounds of this combination of drugs demonstrated a median overall survival of five months. This may not sound like a lot, but as a third-line therapy most metastatic pancreatic patients tend to survive only a month or two, so this is discernible progress.

Finally, the one large cap newsmaker among a sea of small-cap movers making waves this week was Gilead Sciences (NASDAQ:GILD), which had sofosbuvir, its oral experimental hepatitis-C drug, reviewed by the FDA's advisory panel on Friday. Unsurprisingly, given just how well sofosbuvir outperformed the existing therapies in a myriad of hep-C genotypes, the panel voted unanimously, 15-0, in favor of recommending approval for sofosbuvir in genotypes 1 through 4. The move could probably facilitate a quicker review by the FDA and should set Gilead up for a smooth start to sales if approved.

However, as you might have suspected, it wasn't all peaches and cream among the biotech sector this week.

He said, she said ...
Osiris Therapeutics
(NASDAQ:OSIR) had what can only be described best as an "odd week" after it announced on Monday a pathway between it and the FDA for its lead product, Grafix, to obtain a biologics licensing application. Some investors assumed based on this press release that this would mean Grafix would be pulled from the market in the interim until it obtained its BLA. However, Osiris clarified in an additional press release on Thursday that Grafix, which aids in the healing of acute and diabetic foot ulcers, will continue to be sold, and the BLA will only further expand the claims Osiris can make about Grafix, which should allow for better differentiation between other diabetic-ulcer wound-closing therapies. In other words, despite the double-digit weekly decline, there's not much to be seen here.

The disaster du jour
This week's disaster du jour goes to Repros Therapeutics (NASDAQ:RPRX), which fell 27% after it announced that it will delay for a few months its new drug application filing for Androxal for the treatment of male hypogonadism. The reason for the delay, as noted in the press release, is that the FDA would like a year's worth of data to determine the efficacy of the highest dose of Androxal compared to the existing testosterone therapies currently on the market. While investors took this as an opportunity to crush shares, it could represent a great buying opportunity as the FDA's request for additional data could give Repros' drug a chance to significantly outperform its peers in the two additional trials it's running. If that does occur, the FDA has noted that it would possibly give Androxal a priority review.

Fool contributor Sean Williams has no material interest in any companies mentioned in this article. You can follow him on CAPS under the screen name TMFUltraLong, track every pick he makes under the screen name TrackUltraLong, and check him out on Twitter, where he goes by the handle @TMFUltraLong.

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