With the SPDR S&P Biotech Index up 37% 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.

Disappointments come in threes
What I'm about to say is very unlike the biotech sector over the past couple of years, but it was generally a bad week for investors with regard to clinical updates.

The shenanigans began on Monday, with development-stage biopharmaceutical company Prana Biotechnology (NASDAQ: PRAN), which nosedived 76% on the week after announcing that its lead therapy, PBT2, for Alzheimer's disease, failed to meet its primary endpoint of a statistically significant reduction of beta-amyloid plaques in its phase 2 study. Prana's CEO was quick to note that its previous Alzheimer's study involving PBT2 examined levels of unaggregated soluble Abeta peptides in spinal fluid whereas its phase 2 IMAGINE trial examined insoluble plaques which didn't differ significantly from the placebo. While this was meant to inspire confidence in shareholders that PBT2 may not have struck its last chord in Alzheimer's treatment, investors have pretty much discounted any future development in this indication. Keep in mind, though, that PBT2 is still being studied as a Huntington's disease treatment as well.

On the other end of the market cap spectrum (and week), biotech giant Amgen (NASDAQ:AMGN) surprised to the downside on Friday when it announced top-line phase 3 results from its melanoma trial involving talimogene laherparepvec, which is thankfully known as T-Vec for short. Amgen noted that while the primary endpoint of a durable response rate was met, as in previous studies, a key secondary endpoint of improved overall survival was not met, although "there was a strong trend in favor of [T-Vec]." Although T-Vec missed statistical significance in this secondary endpoint, Amgen still plans to pursue further studies to determine if the drug may improve overall survival as a single-agent or combination therapy.  

Rounding out the trio of disappointment was Halozyme Therapeutics (NASDAQ:HALO), which had a wild week after popping by double digits on Monday and then more than erasing those gains with a monstrous 27% loss on Friday.

On Monday, Halozyme announced that its Hylenex recombinant and new formulation of Hylenex met its primary endpoint of non-inferiority of A1C levels following six months of treatment in type 1 diabetics. Furthermore, the rate of overall hypoglycemic events across all treatments groups dropped 12%.

However, on Friday Halozyme announced a temporary halt of a phase 2 trial pancreatic cancer trial currently in the enrollment and dosing stage for PEGPH20 based on a recommendation from an independent data monitoring committee. Directly quoting Halozyme's press release, "The DMC is assessing clinical data that indicates a possible difference in the thromboembolic event rate between the group of patients treated with PEGPH20, nab-paclitaxel and gemcitabine, versus the group of patients treated with nab-paclitaxel and gemcitabine without PEGPH20." Until this safety issue clears up -- and the good news is Halozyme referred to the hold as "temporary" – Halozyme could remain under pressure.

MannKind's wild ride
It was a wild week for clinical-stage biopharmaceutical company MannKind (NASDAQ:MNKD), which plunged by double digits on Monday after it appeared that an approval for its inhaled diabetes medication, Afrezza, looked iffy at best. Following the release of the Food and Drug Administration's panel meeting briefing documents shortly before its meeting with MannKind, investors swarmed the lukewarm excitement surrounding Afrezza.

That pessimism failed to last, though, with the FDA panel voting overwhelmingly -- 13-to-1 for type 1 diabetes and 14-0 for type 2 diabetes -- in favor of recommending Afrezza to be approved for glycemic control of both types of diabetes. Although this doesn't guarantee an approval by the FDA, it certainly makes a strong case for approval come its April 15 PDUFA decision date. I'd still remind investors that MannKind has yet to partner up, so until it does so, and until the FDA's decision is out, it might be best to wait patiently on the sidelines.

Clinical and preclinical onslaught
Lastly, global biopharmaceutical giant Novartis (NYSE:NVS) announced on Thursday that it would be presenting data on 19 (yes, nineteen!) investigational compounds in its oncology pipeline at the annual American Association of Cancer Research meeting, which begins today in San Diego and runs through Wednesday. While there's a gambit of potential data that investors can focus on from Novartis' more than 50 abstract presentations, perhaps the most exciting aspect will be its preclinical data on ALK-inhibitor LDK378 in ALK-positive non-small cell lung cancer. Do yourself a favor and keep your eyes peeled for these abstracts in the upcoming week.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.