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Oncology is the most crowded area of drug research, so there's a bevy of companies trying to come out on top. But the FDA also awards "breakthrough" status for expedited development for treatments in cancer more than any other field.

We asked three Motley Fool experts to hone in on cancer drugs that are now zipping through trials, which could someday prolong the lives of patients. While the failure rate for drugs and vaccines is very high, all the candidates below have shown striking results. Any or all of them could not only help investors score gains, but could eventually turn some cancers from death sentences into manageable chronic illnesses.

Sean Williams: Whether you realize it or not, global cancer drug spending topped $100 billion in 2014, and it could grow to as much as $147 billion by 2018 according to IMS Institute for Healthcare Informatics. For cancer patients, it means potentially game-changing therapies are on the way. For investors, it could mean the opportunity to piggyback on some life-saving medicines.

One cancer drug that I'd suggest investors closely monitor is Geron's (GERN 2.89%) imetelstat, which is targeted at treating myelofibrosis, a rare form of bone marrow cancer that leads to scarring. Currently, there is just one approved myelofibrosis therapy in the United States: Incyte's Jakafi.

Jakafi is a JAK2 inhibitor that's been shown to provide clinical improvement in studies, such as in spleen volume reduction and hematocrit control, but it does not produce partial or complete responses in patients. In other words, it strictly minimizes patient symptoms to improve quality of life.

Geron's imetelstat could change the game. In prior clinical studies, both partial and complete responses were observed in myelofibrosis patients. The downside to imetelstat? It comes with possible liver safety concerns, as the Food and Drug Administration halted studies on the experimental drug between mid-March 2014 and early Nov. 2014. Geron is obviously free to advance the drug now with the hold lifted, but its safety concerns still echo loud and clear.

What makes matters even more intriguing is that healthcare conglomerate Johnson & Johnson is betting up to $935 million on Geron that imetelstat will displace JAK2 inhibitors in the future. It paid Geron $35 million upfront in a collaborative deal this past November, and will deliver $900 million more in undisclosed development, regulatory, and sales milestones.

Imetelstat has serious backers; now it's just a matter of whether or not it works in larger studies.

Todd Campbell: Juno Therapeutics (JUNO) is developing immuno-oncology drugs that reengineer a patient's T-cells to more easily discover and destroy cancer cells. If Juno Therapeutics approach succeeds, it could end up reducing, or eliminating, the use of chemotherapy in cancer patients.

Juno Therapeutics approach is so intriguing that Celgene Corp is spending $850 million to acquire a 9.1 million shares in the company and handing over another $150 million in cash up front in order to partner with Juno Therapeutics on immunotherapies for cancer and autoimmune disease.

Celgene's interest was likely piqued by Juno Therapeutics' JCAR015, a treatment for blood cancer such as acute lymphoblastic leukemia, or ALL. In early stage trials, 87% of adult ALL patients taking JCAR015 went into complete remission.

Those are impressive results, but investors should remember that most cancer drugs fail in the clinic, and that because this was an early stage trial involving only a small number of people, there's no guarantee that this success will be confirmed in future trials. Regardless, Celgene's partnership and JCAR015's potential makes this one that should be on your radar.

Cheryl Swanson: Brain cancer is a tough disease to beat, but the story may be changing for those who have one of the most common types of brain tumors called glioblastoma. Clinical-stage biotech Celldex Therapeutics (CLDX 0.46%) has an experimental drug for this very aggressive cancer; with positive new phase 2 survival data just released, the company could eventually have a winner.

At the American Society of Clinical Oncology's annual meeting last weekend, Celldex released data showing a clear survival benefit for its drug Rintega. The brain-cancer vaccine was awarded the breakthrough designation a few months ago, which could pave the way for an accelerated approval. At twelve months, the ReACT trial data showed that 45% of Rintega patients were alive, versus 31% of control patients. At 18 months, 30% of Rintega patients were alive, versus 15% of control patients.    

Phase 3 data for Rintega is coming later this year. Meanwhile, Northwest Biotherapeutics has a competing glioblastoma candidate called DCVax-L. In contrast to the much more popular CAR-T treatments under development, there's been a lot of uncertainty about cancer vaccines over the years.

But being the dark horses in the race for a cure for cancer has kept the wraps on the prices of these stocks. If positive data continues to come out about their effectiveness, that could sway the critics, and reignite the climb of these two small-cap biotechs.