December 21, 2019
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FDA approves Enhertu for HER2-positive breast cancer

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The FDA granted accelerated approval to fam-trastuzumab deruxtecan-nxki for the treatment of adults with unresectable or metastatic HER2-positive breast cancer who received at least two prior anti-HER2-based regimens in the metastatic setting.

Trastuzumab deruxtecan (Enhertu; AstraZeneca, Daiichi Sankyo) is a novel antibody-drug conjugate with three components: a humanized anti-HER2 immunoglobulin G1 monoclonal antibody with the same amino acid sequence as trastuzumab (Herceptin, Genentech); a topoisomerase 1 inhibitor payload; and a tetrapeptide-based cleavable linker.

The FDA based the approval on results of the phase 2 DESTINY-Breast01 study, presented earlier this month at San Antonio Breast Cancer Symposium.

The open-label, multicenter study included 253 adults with centrally confirmed HER2-positive breast cancer. Patients with stable treated brain metastases were eligible; however, those with a history of significant interstitial lung disease were not.

The intent-to-treat population consisted of 184 women (median age, 55 years; range, 28-96) who received 5.4 mg/kg trastuzumab deruxtecan via IV every 3 weeks.

Patients had received a median six prior treatments (range, 2-27), including trastuzumab (100%), ado-trastuzumab emtansine (Kadcyla, Genentech; 100%), pertuzumab (Perjeta, Genentech; 65.8%), other HER2-targeted regimens (54.3%), hormone therapy (48.9%) or other systemic therapy (99.5%).

Objective response rate by independent central imaging facility review served as the primary endpoint. Secondary endpoints included investigator-assessed ORR, disease control rate, duration of response, clinical benefit rate, PFS, OS and pharmacokinetics.

Researchers reported a confirmed ORR by independent central review of 60.9% (95% CI, 53.4-68). This included 11 complete responses (6%) and 101 partial responses (54.9%). Median duration of response was 14.8 months (95% CI, 13.8-16.9) and median time to response was 1.6 months (95% CI, 13.8-16.9).

Sixty-seven women (36.4%) had stable disease, three (1.6%) had progressive disease and two (1.1%) were not evaluable. This translated to a disease control rate of 97.3% (95% CI, 93.8-99.1) and a clinical benefit rate at 6 months of 76.1% (95% CI, 69.3-82.1).

Researchers observed consistent benefit with trastuzumab deruxtecan across patient subgroups, including those who had prior pertuzumab.

Median follow-up for the survival analysis was 11.1 months (range, 0.7-19.9).

Median PFS was 16.4 months (95% CI, 12.7-not estimable) in the entire intent-to-treat population. Median PFS was 18.1 months (95% CI, 6.7-18.1) for patients with prior brain metastases; however, that group was small (n = 24). Median OS had not been reached.

The prescribing information for trastuzumab deruxtecan includes a boxed warning about the risk for interstitial lung disease and embryo-fetal toxicity.

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An independent adjudication committee determined 25 patients (13.6%) in the DESTINY-Breast01 study developed interstitial lung disease. Twenty cases were grade 1 or grade 2; however, researchers reported one grade 3 case, and four patients had fatal cases believed to be drug related.

Median time to onset of all interstitial lung disease cases was 193 days (range, 42-535); onset of the four fatal cases ranged from 63 to 148 days.

Nearly all patients (99.5%) experienced drug-related treatment-emergent adverse events, the most common of which were low-grade gastrointestinal or hematologic events.

About half (48.4%) experienced grade 3 or higher drug-related treatment emergent events, and 12.5% experienced drug-related serious treatment-emergent events. Drug-related events prompted 14.7% to discontinue treatment.

Twenty-one percent of patients required dose reductions and 28.8% required dose interruption due to drug-related events.

The FDA previously granted breakthrough therapy designation to trastuzumab deruxtecan for this indication.