ASCO: In stomach cancer, AstraZeneca and Daiichi's Enhertu goes where Roche's Kadcyla couldn't

Daiichi Sankyo and AstraZeneca's Enhertu has become the first HER2-directed therapy to show an overall survival benefit for previously treated HER2-positive gastric cancer. (AstraZeneca/Daiichi Sankyo)(Daiichi Sankyo/AstraZeneca)

Daiichi Sankyo and partner AstraZeneca’s Enhertu previously wowed industry watchers with stellar clinical data in heavily pretreated breast cancer, leading to a speedy FDA nod at the end of 2019. Now, the antibody-drug conjugate (ADC) can brag about a first in gastric cancer.

In a pivotal phase 2 study, Enhertu shrank tumors in 42.9% of patients with HER2-positive stomach cancer that had progressed after at least two lines of treatment, more than three times that of the 12.5% posted by investigator’s choice of chemotherapy, according to data presented at the American Society of Clinical Oncology virtual event.

More importantly, Enhertu cut the risk of death by 41% compared with chemo, as patients who got the ADC lived a median 12.5 months, versus 8.4 months for chemo. More than half of Enhertu patients were still alive after one year, while less than 29% of patients in the chemo arm could say that.

The Destiny-Gastric01 trial readout makes Enhertu the first HER2-directed therapy to show an overall survival benefit—the gold standard in evaluating cancer treatments—for previously treated HER2-positive gastric cancer, Antoine Yver, Daiichi Sankyo’s oncology R&D head, said in a statement.

Previously, Roche’s rival HER2 ADC Kadcyla failed to top chemo at extending the lives of gastric cancer patients who had been treated with a first-line therapy. Both Kadcyla and Enhertu use trastuzumab, or Roche’s Herceptin, for the antibody component, but they use different linkers and payloads.

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In further testament to Enhertu’s power, it achieved the success even in patients who had tried Herceptin, which, used in tandem with chemo, has been the standard front-line treatment for HER2 stomach cancer since 2010.

“In addition to the impressive results we saw in HER2-positive metastatic breast cancer in Destiny-Breast01, these results in gastric cancer help further define the role of Enhertu in transforming patient outcomes across multiple HER2 targetable cancers,” AstraZeneca oncology R&D chief Jose Baselga said in a statement.

Enhertu as a third-line HER2-positive gastric cancer treatment was recently granted an FDA breakthrough therapy designation, and the data have been submitted to Japanese authorities for approval.

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AZ and Daiichi obviously have their eyes on Kadcyla, which grew sales by 45% in 2019 to CHF1.39 billion ($1.45 billion). With their late-line breast cancer nod, the two companies are running a head-to-head study against Kadcyla in the second-line setting. The Destiny-Gastric02 study testing Enhertu in second-line gastric cancer is expected to be complete in October.

Since its launch in early January, Enhertu quickly generated sales of $30 million in the first quarter, way ahead of the $18 million estimate Daiichi previously gave FiercePharma, despite a slowdown in new patient starts due to COVID-19.

During the three months, the drug reached 780 accounts, and 515 already have repeated their purchases, Daiichi Sankyo CEO Sunao Manabe said during an investor call in late April. The company’s aiming the drug for 27 billion yen ($252 million) in revenue for the 12 months ending in March 2021, he said.