The American Cancer Society expects 600,920 Americans to die from cancer this year, but Ziopharm Oncology Inc. (NASDAQ:ZIOP) and Celldex Therapeutics, Inc. (NASDAQ:CLDX) aim to lower that figure. Both of these clinical-stage biotechs are developing some exciting new treatment options, and success could lead to monstrous gains over the long run.

Here's a closer look at what they've got cooking in clinical trials to see which stock is a better pick at the moment.

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The case for Ziopharm Oncology Inc.

This clinical-stage biotech doesn't have any products to sell yet, but it's working on a brain cancer treatment with blockbuster potential. Ziopharm's lead candidate is a cancer-fighting CAR-T therapy with two important features its peers lack: a control switch and a penchant for solid tumors.

Kymriah from Novartis and Yescarta from Gilead Sciences are essentially IV bags filled with a patient's own T-cells that have been modified to recognize cancer cell surface targets. Both are approved by the FDA for blood-based malignancies and come with stern warnings because of multiple patient deaths that occurred during clinical trials.

Today's CAR-T therapies aren't toxic themselves, but spilling the contents of millions of cancer cells into the bloodstream all at once can lead to a fatal inflammatory response. Unlike its peers, the activity level of Ziopharm's candidate, abbreviated Ad-RTS-hIL-12, can be controlled by adjusting the amount of another drug, Veledimex, which patients take orally.

Recurrent glioblastoma is a fiendishly difficult-to-treat form of brain cancer that historically claims the lives of a majority of patients within five to eight months following standard treatment. Investors are excited about Ziopharm because the majority of 15 patients treated with Ad-RTS-hIL-12 were still alive at 12.5 months.

After showing data to the FDA earlier this year, the company said the regulator will allow a pivotal trial designed to support a glioblastoma application. We haven't seen Ad-RTS-hIL-12 compared to standard treatment in a head-to-head trial yet, but repeating previous results with a larger population would most likely lead to an approval. With a huge unmet need for better brain cancer treatments, this program could generate more than $1 billion in annual sales for Ziopharm and drive the stock's recent $631 million market cap several times higher in the process.

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The case for Celldex Therapeutics, Inc.

This biotech knows all about unexpected surprises in brain cancer drug development. Its former lead candidate Ritenga had beaten the pants off historical glioblastoma controls but failed to outperform standard chemo when finally measured in a head-to-head trial. Those wounds are a big reason the market continues to overlook the company's new lead candidate, glembatumumab vedotin, or glemba.

This small-cap biotech's market cap of $407 million at recent prices is even lower than Ziopharm's, but glemba is much closer to the finish line than Ad-RTS-hIL-12. A pivotal trial is already underway, and there's a good chance that results expected early next year will send this stock soaring.

Glemba is the first drug of its kind that targets a protein called gpNMB, which is often found on the surface of tumor cells. In a trial with hundreds of breast cancer patients, 16 had tumors with lots of gpNMB and lacked three common targets used by popular treatments. Progression-free survival among triple-negative patients given glemba was 133% longer than those treated with standard chemo.

A repeat performance would more than likely lead to an approval for glemba. The population of triple-negative breast cancer patients is relatively small, but effective new cancer drugs often cost more than $100,000 for a year of treatment. Considering the lack of available treatments for this underserved group of patients, annual glemba sales are expected to top out around $400 million. 

In the numbers

A huge unmet need for new brain cancer treatments gives Ad-RTS-hIL-12 blockbuster potential, which is more than you can say for glemba. Before we call this match for Ziopharm, though, consider the potential cash flows from these companies' respective programs. Ziopharm licenses practically all its technology from Intrexon and The University of Texas MD Anderson Cancer Center.

Celldex owns glemba outright, along with half a dozen additional candidates in clinical trials at the moment. Tack royalty payment burdens to the nightmare logistical scenario Ad-RTS-hIL-12 presents, and its larger peak sales potential doesn't seem quite as large.

We also need to consider that glemba has been measured against standard treatment, and Ziopharm's candidate hasn't. In other words, Celldex has a much better chance of becoming a commercial-stage biotech. Put it all together, and Celldex Therapeutics is the better buy right now, hands down.

Cory Renauer owns shares of Gilead Sciences. The Motley Fool owns shares of and recommends Gilead Sciences. The Motley Fool recommends Celldex Therapeutics. The Motley Fool has a disclosure policy.