Talon: Assessing Marqibo's FDA Odds

SAN MATEO, Calif. (TheStreet) -- An FDA advisory panel convenes March 21 to review Marqibo, a leukemia drug from Talon Therapeutics (TLON). A breakdown of what to expect:

What are Marqibo's chances for a positive panel vote?

Small. I won't guarantee a negative vote; there's always a chance the panel could look favorably on the drug, but the odds are against.

But you're a biotech basher. You hate everything.

It's not just me. The market isn't exactly pricing in good news for Talon -- a bulletin board stock with a $20 million-plus market value.

By the way, I don't hate everything!

I was under the impression that the Marqibo data were strong and that the drug helped leukemia patients who had run out of other treatment options. Isn't this an argument in favor of approving the drug?

It's probably THE argument Talon and its advisors will make during next week's advisory panel meeting. A majority of the 65 acute lymphoblastic leukemia (ALL) patients, all adults over 18, enrolled in the Marqibo study were on their third or fourth lines of therapy. A smaller group of patients in the study had cancer that was no longer responding to five or six previous treatments.

Wait, you just said something vaguely positive about Talon. Keep going.

Thirteen, or 20%, of the 65 ALL patients achieved a complete or near-complete tumor response -- the primary endpoint of the study. The median duration of response for those patients with a CR/CRi was 5.4 months with a median overall survival of 7.4 months.

When stratified by previous therapies, those ALL patients no longer responding to three prior therapies demonstrated a 17% CR/CRi rate from Marqibo therapy; fourth-line ALL patients had a 24% CR/CRi rate to Marqibo.

And these results aren't persuasive enough for an FDA panel to recommend approval?

Meh. Talon's study was single arm, meaning all the patients received treatment with Marqibo. It's difficult to assess patient benefit when there is nothing to compare against Marqibo therapy.

FDA has approved cancer drugs based on single-arm studies in the past, but the agency has recently become a lot more nit-picky about it (and that's doubly true for single-arm registration trials for blood-related cancers.)

No approval standard exists for single-arm cancer trials but a good rule of thumb is a 25% response rate with a six-month duration of response. Marqibo falls short on both measures.

You sound like the old biotech-bashing Adam again.

Hold on! It's not just me telling you something is likely amiss with the Marqibo review, take a look at the warning Talon discloses in its SEC filings:

"In connection with submitting our NDA, we also requested that the FDA grant our application 'priority review,' which would reduce the FDA's review period from the standard 10 months to six months. Although our NDA was accepted for filing under Subpart H accelerated approval regulations, the FDA, upon preliminary review, did not grant our request for priority review, as indicated by the PDUFA date of May 13, 2012. We believe the FDA's determination that our NDA did not qualify for priority review may reduce the probability that the agency will ultimately grant accelerated approval of Marqibo."

That's not encouraging. What does it mean?

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