With the SPDR S&P Biotech Index up 34% year to date, 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.

The beginning of the week kicked off on a relatively high note with good news from both Infinity Pharmaceuticals (NASDAQ:INFI) and Acura Pharmaceuticals (OTC:ACUR).

Infinity rolled higher by 32% on the week after it released positive phase 1 data on IPI-145, its oral PI3K-inhibitor aimed at treating hematological malignancies. The results demonstrated that IPI-145 showed clinical activity in B-cell and T-cell malignancies, which is encouraging enough for Infinity to announce that it'll be testing the experimental compound on chronic lymphocytic leukemia, indolent non-Hodgkin's lymphoma, mantle cell lymphoma, Hodgkin's lymphoma, and T-cell lymphoma. As I suspected, though, Infinity burdened shareholders with another secondary offering later in the week.

Acura Pharmaceuticals was the real standout this week, exploding higher by 83% after it released a new drug known as Nexafed. Acura specializes in developing drugs that are prone to being abused, so its latest offering, Nexafed, an abuse-resistant form of nasal decongestant Sudafed, disallows the ability to synthesize methamphetamine from the drug. As Foolish health-care guru David Williamson notes, Nexafed is wholly owned by Acura, which may mean big profits are right around the corner. 

YM BioSciences (NYSEMKT: YMI) tried its best to give Acura a run for its money, rocketing higher by 78% after agreeing to be purchased by Gilead Sciences (NASDAQ:GILD) for $510 million. With this purchase Gilead will acquire YM's YT387, a myelofibrosis drug that's currently through mid-stage trials. Despite the pop from YM BioSciences, Foolish biotech colleague Brian Orelli isn't all that impressed. Specifically, Brian notes increasing competition and phase 3 uncertainties as reasons for investors to be somewhat cautious about this deal. 

The end of the week, though, wasn't nearly as impressive as it began for Rigel Pharmaceuticals (NASDAQ:RIGL) or Ariad Pharmaceuticals (NASDAQ: ARIA).

Rigel's share price was creamed, losing 20% of its value (although it received a nice rebound on Friday), following results from a mid-stage study with its licensing partner AstraZeneca (NASDAQ:AZN) that rheumatoid arthritis drug fostamatinib underperformed Abbott Laboratories' (NYSE:ABT) Humira in clinical trials. AstraZeneca wasn't ready to throw in the towel yet and expects a bigger trial could yield better results, however, for Rigel which is expecting to rely on royalty and milestone revenue to sustain its business, this is a crucial setback. 

Rounding out the week was Ariad Pharmaceuticals which announced the bittersweet early approval of Iclusig (formerly ponatinib) by the Food and Drug Administration. The once-daily drug is targeted at treating chronic myeloid leukemia and acute lymphoblastic leukemia but will come with an unexpected warning on the box for patients and physicians that it can cause blood clots and liver toxicity. Ariad's orphan drug status will protect sales for some time, but that warning label could also negatively affect sales. Ariad shares dipped 21% on Friday. 

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