TG stock sinks after setback to blood cancer trial

CLL cells (VashiDonsk/CC BY-SA 3.0)

TG Therapeutics has abandoned plans to seek accelerated FDA approval of its ublituximab-umbralisib (U2) combination in chronic lymphocytic leukemia (CLL). The biotech made the decision because its phase 3 overall response rate (ORR) data “were not sufficiently mature to conduct the analysis.”

New York-based TG provided no details of the ORR results in its long-overdue data drop, nor did it say that U2 failed to improve ORR over the comparator. Instead, it the ORR data are currently too immature to analyze, and, as “the timing and the outcome of the ORR analysis” are unclear, it is switching its attention to the progression-free survival (PFS) primary endpoint. 

TG CEO Michael Weiss framed the setback as an “important step” for the company.

“While we are disappointed that we were not able to report positive ORR today, we feel that making the decision to focus on PFS, the primary endpoint for the study, is an important step to getting everyone aligned on the endpoint of this study that matters most to the company and its long-term shareholders. From a timing standpoint, we could have a PFS read out in 2019, and we remain extremely optimistic about the prospects for a successful PFS result,” Weiss said in a statement. 

TG shares fell 30% in premarket trading as investors digested the loss of the accelerated approval opportunity and the read-through for the prospects of the trial hitting its primary PFS endpoint. Although TG pinned the ORR setback on the immaturity of the data, that is a highly unusual explanation that may raise fears that U2 is unlikely to outperform the comparator.

The reevaluation of U2’s prospects continues a process that has been underway for some time. TG finished enrolling patients in the trial last year and was originally due to share the ORR analysis in the second quarter. The target later got reset to the end of the summer. As the September days ticked by without TG delivering data, investors became increasingly nervous, causing the company’s stock to fall by more than 25% over the past month.