The company said it will stop hiring staff required for the expansion. Credit: Sergei Elagin/Shutterstock.

G1 Therapeutics will no longer be investigating its Cosela (trilaciclib) in patients with metastatic triple-negative breast cancer (TNBC) after a Phase III trial failed to meet the primary endpoint.

The North Carolina-based oncology company announced that the Phase III Preserve-2 trial did not meet the primary endpoint of overall survival (OS), with a median OS in the Cosela arm of 17.4 months compared with 17.8 months in the control arm.

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As a result of the 24 June announcement, shares in G1 Therapeutics dropped by 41.1%, with a closing price of $2.48 on 21 June and an opening price of $1.46 on 24 June.

CEO of G1 Therapeutics, Jack Bailey, said: “We will now further our focus on both accelerating and expanding the growth of the extensive-stage small cell lung cancer business to achieve anticipated company profitability in the second half of 2025 and evaluating other myeloprotection uses for trilaciclib. We are also pursuing ex-US partners to expand the use of Cosela globally.”

The Phase III trial (NCT04799249) evaluated the efficacy and safety of Cosela administered prior to chemotherapy (gemcitabine and carboplatin; GCb) in patients with metastatic TNBC.

The safety profile of Cosela with GCb was consistent with prior studies, and no new safety signals were identified.

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As G1 winds down the PRESERVE 2 trial, it also said it will discontinue the anticipated hiring of staff and investment required for the effort of expanding Cosela to the TNBC market.

GlobalData predicts global sales of Cosela to reach $513m in 2030. GlobalData is the parent company of Clinical Trials Arena.

Cosela inhibits cyclin-dependent kinase (CDK) 4/6, which results in suppression of DNA replication and decreased tumour cell growth.

Cosela was approved by the US Food and Drug Administration on 12 February 2021 for chemotherapy-induced myelosuppression.

In April 2023, G1 Therapeutics terminated a Phase III trial of Cosela in colorectal cancer.