With the SPDR S&P Biotech Index up 22% 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.

Mallinckrodt's unexpected buy
Sometimes buyouts come completely out of left field, which is exactly how I'd describe Monday's announcement that Mallinckrodt was going to purchase Questcor Pharmaceuticals (NASDAQ: QCOR), inclusive of unexpired options, for $5.6 billion. The deal, as noted by the press release, would be immediate accretive to Mallinckrodt and be substantially accretive in 2015 and each year thereafter. While it might appear that short-sellers gooses are cooked, shareholders from both sides still need to approve the deal, and there's no guarantee that will occur. In addition, an ongoing investigation by the Food and Drug Administration into the marketing practices of Quesctor over Acthar Gel, its only FDA approved product, could hinder its buyout. This has all the makings of a situation best left avoided.

One giant non-event for MannKind
This upcoming week was supposed to be the culmination of years of hard work for MannKind (NASDAQ:MNKD) and its shareholders. Instead, following an FDA panel meeting that overwhelmingly recommended inhaled insulin therapy Afrezza for approval, the Food and Drug Administration has decided to postpone Afrezza's PDUFA decision date three months until July 15, 2014. While that's not necessarily bad news for the therapy itself as it merely gives the FDA more time to comb over the data, it is bad news for MannKind in that it's another three-month delay in potential bringing its new product to market. This means more cash burned in the meantime. I'm still of the personal opinion that Afrezza will be approved to treat type 2 diabetes (90% of all diabetes cases are type 2), but I'm still up in the air with regard to whether or not it'll be approved as a glycemic control for type 1 diabetes. Either way, MannKind needs a resolution soon so it can turn its attention to seeking out a licensing partner.

Agios's incredible results
Sure, it was only a phase 1 study that hasn't even hit its maximum-tolerated dose yet, but Agios Pharmaceuticals' (NASDAQ:AGIO) AG-221 as a treatment for blood cancers is already a hit with Wall Street and biotech-savvy investors. On Monday Agios announced that its drug had met its primary endpoint of safety and tolerability in an initial phase 1 study. More importantly, though, it demonstrated impressive clinical activity including three complete clinical remissions out of seven evaluable patients. Because complete remissions are so uncommon in blood cancers this new got my head turning, no matter how early in development AG-221 current is. Agios also has a solid development partner in Celgene for AG-221; so if I were you, I'd keep a close eye on Agios moving forward.

Phase 3 glee
The transformation of Alkermes (NASDAQ:ALKS) into a global biopharmaceutical company focused on treating chronic diseases continued this week with it reporting positive late-stage results for aripiprazole lauroxil, a treatment for schizophrenia. According to its press release, Alkermes' phase 3 trial of once-monthly aripiprazole lauroxil met its primary endpoint and demonstrated a statistically significant reduction in the Positive and Negative Syndrome Scale total score at week 12 from baseline relative to the placebo. It also met a key secondary endpoint of improvement from baseline in the Clinical Global Impression -- Improvement Scale at week 12. Alkermes is planning to file a new drug application sometime in the next quarter which could put it in line for an FDA approval by mid-2015.

Hepatitis C of opportunity
Hepatitis C is a big market opportunity for the biopharmaceutical sector, and the latest round of positive data comes from Merck (NYSE:MRK) and its combo therapy MK-5172, an NS3/4A protease inhibitor, and MK-8742, an NS5A replication complex inhibitor. Late in the week Merck announced interim results from its phase 2 C-WORTHy study showing sustained virologic response rates (i.e., no detectable levels of HCV) at 12 and 18 weeks of 90% of greater in cohorts involving genotype 1 treatment-naive patients with liver cirrhosis, treatment-naïve non-cirrhotic patients with HCV and HIV co-infection, and genotype 1 patients who were prior null-responders whether or not they had liver cirrhosis. There's still a lot of data to comb through, but 90% SVRs and higher is certainly worth further research. I'd keep this HCV combo high on your radar, especially if you're a current Merck shareholder