Editor's note: In an earlier version of this column, the item on MELA Sciences contained erroneous information as provided by the U.S. Food and Drug Administration. The agency does in fact enter into formal or binding agreements for experimental medical device clinical trials. MELA's public statements to that effect are correct. The story has been corrected.BOSTON ( TheStreet) -- I will not complain, but keeping up with the volume of your email and tweets is quickly becoming a Sisyphean task. To help catch up, here's a special Thursday edition of the Biotech Stock Mailbag. Tiffany M. emails, "What is your latest take on Ziopharm Oncology (ZIOP) and the start of the phase III study in sarcoma? The company seems to be going against the advice of the FDA. Is that a concern?" Ziopharm is launching a pivotal phase III study of its experimental drug palifosfamide in sarcoma at a time of great uncertainty and debate over how to define and measure clinical benefit in cancer drug studies. I spoke with Ziopharm CEO Jon Lewis Wednesday morning about the study and my sense is the company (with the help of outside experts) has done an admirable job navigating some tricky waters with the palifosfamide study to make it as "approvable" as possible. Does this eliminate all the regulatory risk and worry? No way. Food and Drug Administration statute has long granted accelerated approval to cancer drugs based on clinical trials that measure a drug's ability to delay tumor growth or worsening. This "progression-free survival," or PFS endpoint, was long considered to be a surrogate measure for survival. In other words, if a drug lengthens the time before a patient's tumor starts growing again, that patient would also likely live longer. Drug companies like running cancer drug studies with PFS endpoints because data can be collected and analyzed faster than from studies using overall survival as a primary endpoint. Yet this correlation between PFS and survival benefits in cancer studies is now being challenged. On Tuesday, an advisory panel recommended that the FDA revoke the accelerated approval of Roche's Avastin as a breast cancer treatment because follow-up studies failed to demonstrate a benefit for patients. In 2008, the FDA granted Avastin accelerated approval in breast cancer based on a single study showing the drug delayed tumor growth. It was hoped that follow-on studies of Avastin would both confirm this PFS benefit as well as document that breast cancer patients were living longer. Those subsequent breast cancer studies of Avastin failed to accomplish either objective. In fact, the new studies demonstrated a smaller benefit in delaying tumor growth and no survival benefit for patients. Moreover, patients treated with Avastin were at greater risk for side effects.