Why G1 Therapeutics Got Hammered 42.6% Today

What happened

G1 Therapeutics (NASDAQ: GTHX) reported phase 2 trial data on its lead drug candidate that failed to inspire investor optimism, and shares crashed 42.6% on Thursday.

So what

The company is developing trilaciclib, a cell-preserving drug it hopes to position for use alongside chemotherapy in cancer patients. If the drug can successfully preserve cells usually destroyed by chemotherapy, it could significantly reduce patient burden and improve outcomes.

However, G1 Therapeutics said on Thursday that the overall response rate (ORR) in second-line and third-line small cell lung cancer patients trailed the ORR for chemotherapy alone. Specifically, combining trilaciclib with topotecan, a chemotherapy, produced a 13.3% ORR. The ORR for the topotecan group alone was 23.1%. The disease control rates and progression-free survival (PFS) rates were similar between the two cohorts.

The ORR results more than offset enthusiasm that the trial delivered a statistically significant reduction in the "duration and occurrence of Grade 4 neutropenia," or an abnormally low level of a common type of white blood cell called neutrophils. This latest data follows results from two other midstage trials also reported by management recently.

On Nov. 26, iG1 Therapeutics reported that trilaciclib's use alongside Roche Holdings (NASDAQOTH: RHHBY) Tecentriq and chemotherapy in first-line small cell lung cancer bested Tecentriq plus chemotherapy alone by reducing the risk of neutropenia, anemia, and thrombocytopenia. The triplet produced statistically similar ORR and PFS rates to Tecentriq plus chemotherapy in that study.

On December 4, preliminary data from a Phase 2 trial of trilaciclib plus chemotherapy in metastatic triple-negative breast cancer (TNBC) also was reported. In that trial, interim-PFS for one cycle of trilaciclib was 8.8 months versus 5.4 months for chemotherapy alone. The ORR was 43.3% for the one-cycle regimen versus 29.2% for chemotherapy. When adjusting for chemotherapy cycles, trilaciclib patients experienced myelopreservation benefits, such as a reduced risk of neutropenia.

Now what

A short-acting CDK4/6 inhibitor, trilaciclib attempts to preserve hematopoietic stem cells to improve how the immune system functions in patients taking chemotherapy. Chemotherapy is a brutal treatment regimen because it doesn't differentiate between cancer cells and healthy cells, so there's an important need for therapies that can improve upon it to help patients avoid side effects such as low white blood cell counts.

It remains to be seen, however, if trilaciclib's efficacy will be good enough to shake-up current treatment. The results so far aren't horrible, but they're not slam-dunk good, either, so investors can't be blamed for being disappointed.

Management intends to take all the phase 2 data it's compiling to the Food and Drug Administration (FDA) early next year to discuss how to design registration-supporting trials. Additional data from trials also is expected in 2019 that could restore or further erode confidence.

Overall, this is an intriguing company that investors ought to keep an eye on because its C-suite includes some heavy hitters and the company has a cash stockpile of $390.5 million, which gives it wiggle room.

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Todd Campbell has no position in any of the stocks mentioned. His clients may have positions in the companies mentioned. The Motley Fool has no position in any of the stocks mentioned. The Motley Fool has a disclosure policy.