BOSTON ( TheStreet) --In FDA-speak an "accelerated" drug review can actually be slow.

Talon Therapeutics ( TLON.OB) announced Tuesday that FDA had accepted an "accelerated approval" filing for the cancer drug Marqibo. U.S. regulators will issue an approval decision on Marqibo on May 13, 2012.

But Talon submitted Marqibo to FDA last July 18, which means FDA is taking 10 months to review the drug. Cancer is a serious, fatal disease and nearly all cancer drugs filed for approval with FDA are reviewed in six months. That's known in FDA-speak as a "priority review."

FDA taking longer to review Marqibo means the agency refused to offer the drug "priority review." That's not good, especially for a cancer drug. But Talon is still boasting about receiving an "accelerated review" even through there's nothing really accelerated about a 10-month review.

Let's clear up the confusion.

In the FDA lexicon, accelerated review applies to the clinical trials and endpoints used to study a drug, not the duration of the approval process. It can take years to study a drug in a clinical trial before it's known if a drug benefits patients. For some serious diseases, including cancer, FDA allows companies to shorten the clinical development process by conducting studies using surrogate endpoints.

A surrogate endpoint is an indirect marker or measurement that is believed to be a reasonable substitute for clinically meaningful patient benefit.

An example is a clinical trial of a cancer drug that uses tumor response or tumor shrinkage as a surrogate endpoint for a survival benefit. Under the accelerated review process, the FDA could approve a cancer drug that shrinks tumors in the belief that tumor shrinkage would enable patients to live longer.

A trial that measures tumor shrinkage can be conducted more quickly than a study measuring survival.

If FDA approved a drug under accelerated approval based on a surrogate endpoint, the agency still requires the company to conduct a follow-on study confirming that the drug does indeed demonstrate a real clinical benefit i.e. helps patients live longer. Most recently, Seattle Genetics ( SGEN - Get Report)> received FDA approval for its cancer drug Adcetris by going down this route.

Talon is seeking approval for Marqibo as a treatment for patients to advanced acute lymphoblastic leukemia (ALL), a cancer of the white blood cells. Talon submitted Marqibo for accelerated review based on a phase II study of 65 patients with advanced ALL that was no longer responding to currently available therapies. Tumor response was the primary endpoint in the single-arm study, which means all patients were treated with Marqibo; there was no placebo or control arm for comparison.

Seeking accelerated approval for cancer drugs can be a risky gamble for companies like Talon because FDA often sets a high bar for what it will accept as a reasonable surrogate benefit. FDA does not assume that any rate of tumor shrinkage will automatically help patients live longer, so rejections of cancer drugs under accelerated review are common. Cell Therapeutics ( CTIC - Get Report) fell victim to this trap with pixantrone.

In Talon's case, the risk of FDA rejection is high because the Marqibo data from the pivotal phase II study were underwhelming.

As I mentioned above, cancer drugs almost always receive a six-month "priority review" because FDA considers these drugs major advances in treatment or drugs that provide a treatment where no adequate therapy exists.

A standard review, which is what Talon is getting with Marqibo, means FDA considers the drug to be, at most, a minor improvement over existing therapies.

That sums up Marqibo fairly accurately.

Marqibo is a reformulation of the generic chemotherapy drug vincristine with a history of regulatory failure. Enzon Pharmaceuticals ( ENZN) in partnership with Inex Pharmaceuticals were the first companies to develop Marqibo in the mid-2000s for non-Hodgkin's lymphoma. FDA rejected the drug in January 2005, prompting Enzon to return Marqibo's development rights to Inex (now known as Tekmira ( TKMR)).

In March 2006, Hana BioSciences licensed rights to Marqibo from Inex, choosing to focus development as a treatment for ALL. Underwhelming data from the phase II pivotal study were first released in late 2009, sinking Hana shares. In late 2010, Hana changed its name to Talon Therapeutics. Biotech companies that change their names is almost always a sure sign of trouble.

At one time, Hana/Talon said it was going to file Marqibo for approval in 2010. The filing was delayed until July of this year. As we learned Tuesday, FDA will review the drug in 10 months and issue an approval decision on May 13, 2012.

Talon's "accelerated standard review" of Marqibo isn't going to be easy.

--Written by Adam Feuerstein in Boston.

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Adam Feuerstein writes regularly for TheStreet. In keeping with company editorial policy, he doesn't own or short individual stocks, although he owns stock in TheStreet. He also doesn't invest in hedge funds or other private investment partnerships. Feuerstein appreciates your feedback; click here to send him an email.