BOSTON ( TheStreet) -- Welcome to this week's Biotech Stock Mailbag. @WilliamPShelley kicks it off with a tweet concerning Celldex Therapeutics ( CLDX).

"What do you think about $CLDX. Volume is up in these 2 days and over $4!"

Celldex was once forgotten but, apparently, no longer. I highlighted Celldex and its breast-cancer drug CDX-011 in my wrap-up of the JPMorgan Healthcare Conference. Data from a phase II breast cancer study of CDX-011 in the spring is Celldex's next important catalyst. A few more details:

CDX-011 is a monoclonal antibody drug conjugate. The antibody portion targets cancer cells that express a protein known as GPNMB shown to correlate with poorer outcomes in breast cancer patients. When the CDX-011 antibody attaches to GPNMB-expressing tumor cells, it releases a toxic chemotherapy payload. This "drug conjugate" was licensed from Seattle Genetics ( SGEN) and is the same one used in the newly approved lymphoma drug Adcetris.

CDX-011 was previously studied in a phase I/II study of advanced and metastatic breast cancer patients, with data reported at the 2010 American Society of Clinical Oncology annual meeting. Forty-two breast cancer patients were enrolled in the study, all heavily pre-treated with a median of seven prior breast-cancer therapies.

In the phase II portion of the study, nine of 26, or 35%, of patients were progression-free after 12 weeks of treatment. Two patients were excluded from the analysis because they discontinued the study without tumor progression prior to 12 weeks.

Twelve percent (4/33) of patients in the phase II portion of the study had a partial response to CDX-011 therapy, although just two, or 6%, of those partial responses were independently confirmed. Another 19 patients, or 58%, were stable following treatment with CDX-011.

The study enrolled 10 breast cancer patients with so-called triple negative disease, which is very difficult to treat. Two of the patients, or 20%, responded to CDX-011 therapy, with one partial response independently confirmed.

Importantly, researchers analyzed tumor samples from some patients in the study to measure the level of GPNMB expression. They found that patients with tumors over-expressing GPNMB responded more strongly to CDX-011 therapy, with response rates ranging from 20% to 33%, depending on the level of GPNMB expression. No patients responded if their tumors didn't express GPNMB.

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