With the SPDR S&P Biotech Index up 47% 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.

Not to purposely duplicate last week, but this holiday-shortened week left our plate filled with nothing but good news from the biotech sector, so let's dive right in.

A trio of positive trials
Perhaps nothing was more exciting this week than Orexigen Therapeutics' (NASDAQ: OREX) announcement on Monday that its long-term safety study of weight control therapy Contrave demonstrated no increased risk of heart attack or adverse side effects in its 9,800 patient Light Study. This is important, because Contrave was actually rejected by the Food and Drug Administration in Jan. 2011 because of potential cardiovascular safety concerns, and this interim analysis seems to demonstrate otherwise. It could lead to a U.S. approval for Contrave and also give the company the upper-hand on beating its peers to an EU approval having already completed a long-term safety study. If I were you, I'd keep your eyes on Orexigen and Contrave.

Merrimack Pharmaceuticals (MACK 0.14%) joined the impressive data bandwagon by turning the tables on experimental breast cancer drug MM-121 and reporting positive data after sending mixed signals just weeks ago. According to two mid-stage trials, Merrimack reinforced its findings that select biomarkers, such as ErbB3, do appear to play a role in interfering with cancer growth. Although Merrimack isn't going to garner as large of a treatable patient population as it would like, it could, nonetheless, become the go-to treatment for patients with these select biomarkers if approved. Keep in mind that we're still quite a way off from that approval, but it was certainly a positive week for Merrimack shareholders.

Likewise, Cubist Pharmaceuticals (CBST.DL) reported positive late-stage data for CXA-201, known better as ceftolozane/tazobactam, for the treatment of complicated urinary-tract infection. The study demonstrated that CXA-201 wasn't inferior to the current standard of treatment, levofloxacin, and Cubist noted that while the study wasn't designed to determine superiority, there were signs that would point to CXA-201 as a possibly superior treatment to levofloxacin. CXA-201 has the potential to gain other indications, including the treatment of intra-abdominal infections and hospital-acquired/ ventilator-associated bacterial pneumonia. Not to sound like a broken record, but it's an antibiotic that could surprise investors if approved.

Why thank you, may I have another?
Although it happened late last Friday and sneaked under my radar, I have to mention that Amgen (AMGN -1.33%), which recently completed its acquisition of Onyx Pharmaceuticals, received an expanded FDA approval for Onyx's drug Nexavar to treat patients with metastatic, progressive, differentiated thyroid carcinoma -- or DTC -- refractory to radioactive iodine treatment. DTC isn't too common of a cancer, so it's not going to knock Amgen's sales out of the park, but it is the only FDA-approved treatment for this aggressive form of thyroid cancer, thus giving Amgen sole possession of this subset of patients.

Racking up milestones
Finally, Isis Pharmaceuticals (IONS -1.44%) galloped to the upside after announcing that it had begun a phase 1 trial utilizing ISIS-GSK3, a partnered compound with GlaxoSmithKline designed to treat an undisclosed but common viral infection. The start of this trial entitles Isis to receive a $3 million milestone payment from GlaxoSmithKline, and keeps it in the driver's seat until the completion of phase 2 proof-of-concept trials upon with Glaxo has the rights to relicense the program and continue to develop the compound. With 30 compounds currently in its pipeline, Isis is rich with partnerships and proprietary technology. It's a name I strongly suggest you keep your eyes on in the biotech sector.