With the SPDR S&P Biotech Index up 25% 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.

It was a week of predominantly large moves with two FDA rulings (sending one company higher and the other lower), and three big clinical updates.

Beginning with the FDA rulings, nothing stands out more to me than the approval by the Food and Drug Administration of Biogen Idec's (NASDAQ:BIIB) Tecfidera (previously BG-12) to treat relapsing multiple sclerosis. In trials, Tecfidera demonstrated far better efficacy with significantly fewer side effects than currently approved oral MS medications. Aubagio, which is made by Sanofi carries a black box warning regarding liver complications, and Gilenya, made by Novartis, can cause serious cardiovascular complications. Tecfidera received the thumbs up for approval from the European Medicine Agency's panel last week and could have a billion-dollar drug in its pipeline as rapidly as 2014 if it gains approval in the EU as well. 

Conversely, United Therapeutics (NASDAQ:UTHR) needs more than a rabbit's foot to get a little luck on its side when it comes to gaining approval for its oral pulmonary arterial hypertension drug, Treprostinil. On Monday, the company received its second complete response letter in the past six months denying its approval. If you recall, I thought it odd how quickly United Therapeutics had resubmitted its new drug application, especially when it appeared the FDA would like to see the company run additional clinical tests to support its six-minute walking distance data. Until United Therapeutics caves into further trials, Treprostinil will remain a "what if" for investors. 

In terms of late-stage data, we had one company explode higher, one stand pat, and one get absolutely eviscerated this past week.

Soaring to the heavens this week was Repros Therapeutics (NASDAQ:RPRX), which reported Thursday that Androxal, its secondary hypogonadism treatment, met both primary endpoints in late-stage trials. Repros shares imploded two months ago when it noted it'd be delaying its data report for a few months because of an anomalous patient pool which appeared to exhibit above average results. Following the OK from the FDA to continue its data analysis in February, the end result, according to Repros, was that 79%-83% of treated patients were in the normal testosterone range (primary endpoint was 75%). Androxal also met the sperm primary endpoint that it exhibit non-inferiority to the placebo by a margin of 20% or less. Repros is more of less trading at levels it was at when it had its "boo-boo" in late January, so it could indeed have room to run higher as my Foolish colleague Brian Orelli noted. Shares advanced 83% this week.

Trius Therapeutics (UNKNOWN:TSRX.DL) reported what I felt was phenomenal data for its late-stage acute bacterial skin and skin structure infection drug, Tedizolid, on Monday -- yet the stock barely moved. In trials, the ABSSSI drug handily mopped the floor with Pfizer's Zyvox, meeting both its primary endpoint of reducing lesion size, and secondary endpoints of a sustained clinical response and positive investigative assessment at the end of the therapy. Tedizolid, an oral medication, can be administered in just six days compared with Zyvox's 10-day regimen, which makes it a clear choice to outperform both domestically and overseas. This is a name I think you should have on your Watchlist. 

Finally, Ziopharm Oncology (NASDAQ:ZIOP) imploded, with shares falling 62% on the week after the company announced it would be discontinuing its late-stage drug Palifosfamide for the treatment of metastatic soft tissue sarcoma. The independent data monitoring committee suggested that Ziopharm follow-up with existing patients to see if there was an improvement in overall survival, but when it was apparent that there wasn't a statistical advantage to Palifosfamide over the placebo in terms of progression-free survival, Ziopharm's management decided to pull the plug on the drug altogether with regard to metastatic soft tissue sarcoma. Instead, Ziopharm plans to focus entirely on its synthetic biology programs which are much earlier along in the development process.