With the SPDR S&P Biotech Index up 44% 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.

Usually I start every week off with good news and slowly careen you into the week's disaster stories. Well you won't have to worry about that this week, because it's all good news -- so let's get this weekend started off on a positive note!

Europe brings good tidings
Perhaps no company breathed a bigger sigh of relief this week than Ariad Pharmaceuticals (NASDAQ:ARIA) which, on Friday, received a positive opinion from the European Medicines Agency regarding its leukemia drug Iclusig, which is currently on sales hold in the United States. According to the EMA's decision, it's recommending Iclusig continue to be prescribed, although it's laid out some precautionary measures to reduce the risk of blood clots in patients. These include not prescribing Iclusig to patients with a history of heart attack, examining patients' cardiovascular history before beginning treatment with Iclusig, regulating patients with high blood pressure, and monitoring patients constantly for any adverse effects. Although we've heard no word in the U.S. on how the Food and Drug Administration will proceed with regard to Iclusig, the EMA's move could serve as a model for the FDA to follow. Shares soared 52% this week.

Biogen Idec (NASDAQ:BIIB), on Friday, also got a dose of good news courtesy of the Committee for Medicinal Products for Human Use in the EU which determined that multiple sclerosis drug Tecfidera does qualify as a "new active substance," giving it a decade's worth of exclusivity which will free it from any potential generic competition. Tecfidera's sales have soared since it was approved earlier this year and could easily reach blockbuster status next year. With Biogen Idec shares nearly doubling since its approval you might be considering pulling some profits from the table, but I would suggest that you're only seeing the tip of the iceberg when it comes to Tecfidera's potential. Biogen shares headed higher by 17% on the week -- not bad for a $67 billion company!

Horizon goes shopping
Giving Ariad a run for its money was small-cap Horizon Pharma (NASDAQ:HZNP), which scorched higher on the week by 42% after announcing that it would be purchasing the U.S. rights to arthritis drug Vimovo from AstraZeneca for $35 million. Horizon will also be responsible for annual royalties of up to $7.5 million to Pozen until its intellectual property patents run out as well. Normally you won't see this sort of spike associated with a purchase, but it should help move Horizon quickly toward profitability as its share price hike has demonstrated this past week.

Regeneron tacks on another approval
Biotechnology juggernaut Regeneron Pharmaceuticals (NASDAQ:REGN) delivered a double-dose of good news for investors late in the week. On Friday, it and Bayer announced that they had received approval to treat macular edema following central retinal vein occlusion with Eylea in Japan. On Thursday, perhaps the more exciting news was it and Sanofi's first positive late-stage trial results for sarilumab, a treatment for rheumatoid arthritis in cases where patients are unresponsive to methotrexate treatment. The study showed an improvement in the signs and symptoms of RA ranging from 58% to 66% based on dosage compared to 33% for the placebo. Also, there was improvement in physical function and inhibition of progression of structural damage according to Regeneron's press release. Shares of Regeneron ended the week higher by 5%.

Preclinical pop
Finally, to close out your week with a little preclinical excitement, synthetic vaccine maker Inovio Pharmaceuticals (NASDAQ:INO) on Wednesday reported positive preclinical results for a DNA-based vaccine to treat Middle East Respiratory Syndrome, which has been fatal in 42% of the 153 identified cases since last year. According to Inovio's press release, it was able to develop the DNA vaccine using its SynCon vaccine platform and its proprietary Cellectra electroporation delivery system and noted positive neutralizing responses in mice. Although the reaction in mice could differ from how the vaccine interacts with humans, it's still a nice start for Inovio. Shares gained 7% for the week.

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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