What happened

After reporting that it will no longer consider an accelerated pathway to approval of a combination drug therapy in clinical trials, TG Therapeutics (TGTX -0.89%) shares are tumbling 34% at 11:30 a.m. EDT on Tuesday.

So what

Until now, the company had been hoping that a phase 3 trial of its combination of ublituximab and umbralisib (U2) in chronic lymphocytic leukemia (CLL) would produce compelling enough overall response rates to allow it to file for accelerated approval.

A man hides his face in front of a wall with light bulbs drawn on it.


Today, that hope was dashed when management said independent monitors of the study couldn't conduct an interim analysis of overall response rate, a secondary trial endpoint, because the "data were not sufficiently mature."

No longer convinced that overall response rate can win over FDA regulators, TG Therapeutics will now rely solely on the study's primary endpoint -- progression-free survival -- to secure an approval. Unfortunately, data on progression-free survival won't be available until next year, at the earliest.

Now what

The monitors also reviewed the safety data and recommended the trial progress. The two-drug combination (U2) is being evaluated head to head against Gazyva, a Roche Holdings (RHHBY 1.45%) drug with $183 million (at current exchange rates) in sales in the first half of 2018, and chlorambucil, a chemotherapy.

If the doublet outperforms Gazyva, then TG Therapeutics has a shot at a therapy that could generate nine figures in annual revenue; however, given the uncertainty of achieving progression-free survival benefits and the delayed timeline to knowing how effective this combination really is, it's understandable that investors are disappointed.