With the SPDR S&P Biotech Index up 25% 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.

Source: James McCauley, Flickr.

Call it waiting for the last minute, but Biogen Idec (NASDAQ:BIIB) wowed investors in after-hours by announcing that Eloctate, the company's hemophilia A therapy designed to extend the time between prophylactic infusions for adults and children, was approved by the Food and Drug Administration. As the only hemophilia A treatment designed to reduce the frequency of bleeding episodes, the approval of Eloctate represents a potentially meaningful improvement in patient quality of care. In other words, instead of 150 to 180 infusions per year hemophilia A patients may now only need somewhere between 70 and 120. Biogen Idec is also awaiting word on a marketing decision in Canada, Australia, and Japan. With peak sales estimates averaging about $1.5 billion, it looks as if Biogen just scored another big victory for investors and patients.

The trifecta of disappointment
In addition to our usual gambit of clinical data and rulings this past weekend also featured dozens of biotech companies presenting data at the American Society of Clinical Oncology's annual meeting. While a number of companies delivered positive data, the most memorable events were the three failed and/or questionable studies that emerged.

Perhaps no company took it on the chin more than Puma Biotechnology (NASDAQ:PBYI) which lost a quarter of its value this week after reporting phase 2 data on PB272 (also known as neratinib), an investigational therapy for patients with metastatic breast cancer that's spread to the brain. The way I saw it, there were two particularly worrisome figures within its results. First, the number of grade 3 neratinib-related diarrhea events were fairly high. Patients which received a low-dose of loperamide help counter the drug-induced diarrhea still had grade 3 diarrhea 21% of the time, while those patients who didn't take loperamide reported grade 3 diarrhea 29% of the time. Furthermore, the end results, while showing a median of 1.9 months of progression-free survival and a median overall survival of 8.7 months, still only produced three patients out of 40 (7.5%) that had a partial response. I fully understand that metastatic breast cancer that has spread to the brain is very difficult to treat, but investors were clearly expecting a better partial response rate from Puma's lead drug candidate.

Trailing not far behind Puma was Clovis Oncology (NASDAQ:CLVS) which sunk 22% for the week after reporting initial data on CO-1686, the company's non-small cell lung cancer drug targeting the T790M dominant resistance mutation. As Clovis noted, initial estimates of median progression-free survival was better than 12 months and CO-1686 delivered an objective response rate of 58% over 40 evaluable patients. With these results you'd think Clovis shares would have soared higher instead of falling. However, the data set also showed that a handful of patients in its study had to be placed on insulin following bouts of high blood sugar. This led Citigroup analyst Yaron Weber to declare that AstraZeneca's investigational NSCLC drug AZN9291 is superior to CO-1686 based on its now preferential safety profile. While CO-1686 is still a viable investigational therapy for NSCLC patients that are T790M-positive, it brings back up the fact that Clovis has had trouble in the past getting its lead drug past mid-stage trials.

Finally, ASCO showed that even the big boys can report a dud now and then. In a study that involved more than 8,000 patients dubbed ALTTO, GlaxoSmithKline (NYSE:GSK) and Roche reported that the addition of Glaxo's Tykerb as an adjuvant therapy to Roche's Herceptin as a treatment for HER2-positive early stage breast cancer did not meet the primary endpoint of a statistically significant improvement in the four-year disease-free survival rate. According to the data, 86% of patients in the Herceptin control arm did not have their cancer return while the Herceptin/Tykerb arm improved slightly to 88%. This failure was also a reason why Puma Biotechnology had such a rough week since PB272 is an adjuvant therapy, and adjuvants aren't necessarily assured of hitting their primary endpoint as we saw this week.

Waving the green flag
After waving the caution flag for about two months Halozyme Therapeutics (NASDAQ:HALO) on Wednesday evening announced that the FDA had removed its clinical hold on investigational pancreatic therapy PEGPH20 allowing Halozyme to continue enrolling and dosing patients. Study 202 was originally halted because of the possibility of elevated thromboembolic events, but with revised protocol, and a positive recommendation from the independent data monitoring committee that the trial should resume, Halozyme got the green flag from the FDA. With MabThera SC approved in Europe and Halozyme looking as if it'll turn the corner to profitability as soon as next year, I'd suggest that now is the time to get this company on your radar.

Source: GW Pharmaceuticals.

A different type of "green" flag
Finally, highly controversial biopharmaceutical company GW Pharmaceuticals (NASDAQ:GWPH), which discovers cannabinoids for marijuana plants and uses them to alter biologic functions via the body's cannabinoid receptor system, roared higher on Friday after announcing that the FDA had granted investigational drug epidiolex fast-track status for Dravet Syndrome, a rare and treatment-resistant form of childhood epilepsy. The fast-track designation will give GW more one-on-one communication with the FDA regarding epidiolex's development and could lead to a priority or expedited review process.

There really isn't a company out there that does as much with cannabinoids as GW Pharmaceuticals, but it also has to overcome the huge objections of patients and physicians of using marijuana-based products as a treatment. In addition, its lead product, Sativex, which is currently approved throughout much of Europe to treat spasticity associated with multiple sclerosis, has sold very poorly. Until further notice, I'd suggest investors "park their cars in the pits" despite this fast-track designation until GW's bottom line proves otherwise.