Over the past month biotech stocks have been absolutely bludgeoned, with the SPDR S&P Biotech ETF down 22.4%.

I've offered my two cents on the subject previously and surmised the the dramatic fall is based on some combination of unrealistic post-IPO valuations, far too much credence being paid to wholly clinical pipelines, and far-reaching buyout valuations that simply don't make much sense. We all knew the sector couldn't go up forever, and biotech investors might now be learning that lesson the hard way.

But, not every biotech stock has fallen flat on its keister. In fact, a handful have actually risen in the wake of the big dip in the SPDR S&P Biotech ETF. Here's the story behind five unlikely stocks that are bucking the biotech sell-off and rising to the occasion.

Endocyte (NASDAQ: ECYT): up 35.4%
Despite falling well off its highs, Endocyte shares have handily outperformed the sector after the company reported a double-dose of positive news surrounding cancer hopeful vintafolide. In Europe, where vintafolide is known by the brand name Vynfinit, the Committee for Medicinal Products for Human Use issued a positive opinion for the conditional marketing authorization of the drug to treat platinum-resistant ovarian cancer patients. The CHMP also issued positive opinions on its two companion imaging components.

At home, the combination of vintafolide and docetaxel met its primary endpoint in a phase 2b nonsmall cell lung cancer trial known as TARGET. Overall, the vintafolide arm demonstrated a disease-worsening or death risk reduction of 25% compared to the placebo arm with docetaxel alone.  

Vintafolide looks like it could be a big winner for Endocyte and collaborative partner MerckWith peak sales estimates north of $1 billion, it remains a developing drug worth monitoring.

Source: Questcor Pharmaceuticals.

Questcor Pharmaceuticals (NASDAQ: QCOR): up 23.8%
An easy way to buck the downtrend is to be bought out, which is exactly what happened to the maker of Acthar Gel, Questcor Pharmaceuticals.

Mallinckrodt will fork over $30 in cash and 0.897 shares of common stock per Questcor share in exchange for Questcor, valuing the company at $5.6 billion. With the deal expected to be immediately accretive to earnings, and significantly accretive by 2015 and thereafter, it seemed like a slam dunk for both boards.

However, investors should keep in mind here that neither company's shareholders have voted to approve the deal, and the ongoing investigation by the Food and Drug Administration into the marketing of Acthar Gel could very easily stymie Mallinckrodt's buyout.

MannKind (NASDAQ:MNKD): up 11.7%
It's been an absolute roller-coaster ride for shareholders in clinical-stage biotech company MannKind, which looked doomed after the release of FDA panel briefing documents in late March that contained rather modest efficacy language for Afrezza, MannKind's experimental inhaled insulin therapy. Shares, however, skyrocketed after the recommendation for approval just days later from the FDA panel by a vote of 14-0 for type 2 diabetes and 13-1 in type 1 diabetes for Afrezza.

Dreamboat (2nd generation) inhaler, Source: MannKind.

But, the thrill ride didn't end there. With an expected PDUFA decision less than 10 days away, the FDA earlier this month announced that it would push back its decision to approve or deny Afrezza to July 15. This three-month delay crushed the hearts of options traders and put up an obstacle to MannKind's hopes to get its inhaled insulin therapy on the market sooner rather than later. While I still anticipate an approval, there are still a number of questions left to be answered, including who MannKind plans to partner with. Until these questions are answered I'd suggest taking a seat in the bleachers and grabbing some popcorn.

Geron (NASDAQ:GERN): up 3.3%
I guess if there's any consolation to Geron shareholders it's that their shares managed to not be pummeled any further over the trailing month.

The big cement block on the feet of every Geron shareholder is the ongoing clinical hold of imetelstat, an experimental therapy designed to treat myelofibrosis, polycythemia vera, and multiple myeloma. In its company-run polycythemia vera study, persistent low-grade liver function abnormalities were noted, which has the FDA concerned about longer-term use of the therapy and/or whether the liver abnormalities are reversible.

Following Geron's more than 60% tumble, its remaining shareholders are focused on the potential that a release of the clinical hold, perhaps with tougher dosing regulations and/or safety warnings, could send shares markedly higher. Let's not forget, in an investigator-sponsored trial imetelstat delivered a complete response in a myelofibrosis patient, which is extremely rare. But imetelstat is all Geron has, so the drug's rejection by the FDA would leave Geron nothing more than a shell company with cash.

Agios Pharmaceuticals (NASDAQ:AGIO): up 1.2%
Lastly, we have the relatively unknown Agios Pharmaceuticals, which is just above the flatline after reporting stellar early stage data on AG-221, its oral inhibitor of IDH2 mutations for patients with blood cancers.

I know this is an early stage drug that hasn't even hit its maximum tolerated dose as of yet, but these results were simply phenomenal in its initial cohort. Although its primary endpoint of safety and tolerability were met, the real excitement came from achieving an objective clinical response in six of seven evaluable patients. Not only was an objective response noted, but three of the six patients had a complete response which is rare for blood cancers.  

Agios is partnered up with Celgene to develop AG-221. Like Endocyte with vintafolid, such high-profile partnerships provide the financial backing and marketing know-how to make these drugs successful if they wind up reaching the market. I'd keep your eyes squarely on Agios moving forward.