With the SPDR S&P Biotech Index up 38% 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.

Last week was dominated by a mountain of data coming out of the American Society of Clinical Oncology's annual meeting in Chicago. In fact, there was so much information to plow through that, in a separate article, I discussed the five most important and intriguing studies unveiled at ASCO. I encourage you to review that article to get an idea on what disease treatments were in high demand this year.

Having covered the goings-on at ASCO already, I propose we look at five additional newsworthy stories this week in the biotech sector.

On Wednesday, Avanir Pharmaceuticals (NASDAQ: AVNR) received good news from the Food and Drug Administration, which OK'd an accelerated development pathway for pre-investigational neuropathic pain drug AVP-786. The accelerated approval was based on data from AVP-923 and will allow Avanir to conduct minimal preclinical testing before advancing onto human trials. This saves the company time and, more importantly, precious cash. I would, however, caution against getting too excited, as even this accelerated development puts this drug, which isn't even in clinical trials yet, years away from a possible approval.

You can also chalk up an early week win for Aegerion Pharmaceuticals (NASDAQ: AEGR) and its homozygous familial hypercholesterolemia, or HoFH, drug known as Juxtapid. The drug, which is known as Lojuxta in Europe, received a positive opinion from the Committee for Medicinal Products for Human Use and is poised to get a decision on approval from the European Medicines Agency sometime in the third quarter. In the U.S. Aegerion recently announced plans to boost the annual price on its breakthrough pill from $235,000 to $295,000, but consider me still not fully sold that this will be enough to justify Aegerion's insane share price spike or even get the company solidly into the black.

Fat-busting pill producer Arena Pharmaceuticals (NASDAQ: ARNA) and its shareholders received the news they've been waiting about a year to hear -- Belviq will be commercially available as of this Tuesday. Belviq had been on hold as it was awaiting scheduling from the Drug Enforcement Agency, though was recently found to have a low potential for addiction. Now the real battle over obesity begins between Arena and VIVUS's Qsymia which has seen sales struggle. Both companies will need insurers to step up and cover their chronic weight-management pills if they're to be successful.

It wasn't nearly as exciting a week for Rigel Pharmaceuticals (NASDAQ: RIGL), which regained full rights to rheumatoid arthritis pill Fostamatinib from AstraZeneca on Tuesday. The pair actually reported a statistically significant ACR20 response rate at 24 weeks in two trials, but the data isn't expected to be conclusive enough to gain FDA approval. AstraZeneca, not wanting to spend any more on the program, took a $140 million charge and returned all licensing back to Rigel. With the prospect of high trial costs and a drug which did well, but perhaps not well enough to compete with competition already on the market, Rigel is now in a tough position and is worth avoiding at all costs.

Finally, clinical-stage cancer drug developer AVEO Pharmaceuticals (NASDAQ: AVEO) certainly shook things up this week by announcing it will be laying off 140 employees or 62% of its staff to cut its expenses and extend its existing cash balance for another two years. Furthermore, AVEO outlined its plan to focus on developing its lead cancer drug, Tivozanib, for breast and colorectal cancer, but not for renal cell carcinoma. Management noted that it doesn't believe the FDA would approve Tivozanib for RCC without the need for additional testing that it isn't prepared to do right now, with Astellas Pharma having backed out of their development partnership. 

Who will win the obesity drug market?
Can VIVUS pick up its lagging sales and fend off the competition, or will Arena Pharmaceuticals reign supreme in the obesity space? If you're in the dark, grab copies of The Motley Fool's premium research reports on VIVUS and Arena Pharmaceuticals to stay up to date. Senior biotech analyst Brian Orelli gives investors the must-know information, including an in-depth look at the obesity market and reasons to buy and sell both stocks. Click now for an exclusive look at Arena and VIVUS -- complete with a full year of free updates -- today.

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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