Biotech Stock Mailbag: Celldex, TG Therapeutics, Sarepta

TOWN, STATE (TheStreet) -- Welcome to this week's Biotech Stock Mailbag. Before I get to your emails and tweets about Celldex Therapeutics (CLDX), TG Therapeutics (TGTX), Sarepta Therapeutics (SRPT), ImmunoCellular Therapeutics (IMUC) and Osiris Therapeutics (OSIR) (A lot of "Therapeutics" this week!), I have a request:

Please enter my FDA Drug Approval Contest. It's a ton of fun. The more entries I get, the more data I have to crunch about sentiment for upcoming drug approvals that I can share with you. I'm looking for at least 100 entries before end of trading today. I'm almost there, so if you haven't entered yet, check out my column on the contest and post your entries in the comment section. Who knows, you may just win!

Moving on to your emails and tweets:

@ColfaxCapital asks, "What are your thoughts on $CLDX? In less sick population, ORR should be attainable; PFS goal might be aggressive, unknown?"

Colfax is referring to Celldex Therapeutics and the design for the accelerated approval trial disclosed Thursday morning for its experimental monoclonal antibody drug conjugate CDX-011.

Celldex plans to enroll approximately 300 patients with triple-negative breast cancer with tumors that also over-express the protein GPNMB. [The antibody portion of CDX-011 hones in on GPNMB-expressing tumors.] The patients will be randomized 2:1 to receive treatment with CDX-0-11 or Roche's Xeloda (capecitabine.) The primary endpoints are overall response rate or progression-free survival. Celldex says it will be able to submit for FDA approval (accelerated approval) as long as one of the two endpoints are met.

Celldex chose not to pursue a Special Protocol Assessment (SPA) agreement with FDA for the trial because regulators were copacetic with either overall response (with durability) or PFS as clinically meaningful endpoints given the lack of current treatment options for triple-negative breast cancer, Celldex chief medical officer Tom Davis told me in an interview. Pfizer (PFE) employed "either/or" primary endpoints for its pivotal trial of the lung cancer drug Xalkori, so there's precedent for this design, added Davis.

The study will begin enrolling patients in the second half of the year, with accrual taking approximately 18 months. Top-line data will likely be approximately nine months later.

In addition to having triple-negative breast cancer that over-expresses GPNMB, the patients in the study will also be resistant to prior treatment with anthracyclines and taxanes. In other words, the patients in the accelerated approval trial will enter with less advanced disease than the patients who participated in the previous phase II study of CDX-011. [I wrote about the results from the CDX-011phase II study when they were presented last December.]

Celldex powered the new study with the assumption that Xeloda-treated patients (the control arm) will have a 15% response rate and PFS of 4 months. The company believes CDX-011 can double response rate to 30% and improve PFS by 2.25 months.

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