Early Study Findings Show Novel Drug Elicits Promising Results in Metastatic Breast Cancers

Treatment with HER3-DXd (patritumab deruxtecan) was associated with inducing encouraging responses in patients with HER3-expressing metastatic breast cancer or metastatic triple-negative breast cancer.

Data presented at the 2022 American Society of Clinical Oncology Annual Meeting demonstrated that the novel drug, an HER3 directed antibody drug conjugate, elicited an objective response rate (percentage of patients whose disease partially or fully responds to treatment) of 30.1% at a median follow-up of 31.9 months. Of note, treatment with HER3-DXd only resulted in partial responses.

The median duration of response (or time a disease responds to treatment without getting worse) in this cohort was 7.2 months. The median progression-free survival (time a patient lives without disease progression) was 7.4 months and the median overall survival (time a patient is alive regardless of disease progression) was 14.6 months.

In patients with HER3-high metastatic triple-negative breast cancer, the objective response rate was 22.6%. Again, all responses to treatment were partial. The median duration of response to treatment in this group was 5.9 months, with a median progression-free survival of 5.5 months and a median overall survival of 14.6 months.

In patients with HER3-high, HER2-positive metastatic breast cancer, the objective response rate was 42.9%. All responses were partial. The median duration of response was 8.3 months, with a median progression-free survival of 11 months and median overall survival of 19.5 months.

“Significant unmet need still remains for the treatment of patients with metastatic breast cancer and new treatment strategies need to be continuously explored,” lead study author Dr. Ian E. Krop, chief clinical research officer and associate cancer center director for clinical research at Yale Cancer Center in New Haven, Connecticut, said in a press release announcing the findings. “Results from this trial show that (HER3-DXd) produces clinically meaningful and durable antitumor activity in patients and further study is warranted to further evaluate the efficacy and safety of this HER3-directed (antibody drug conjugate) across patients with HR-positive/HER2-negative, HER2-positive, and (triple-negative breast cancer).”

An analysis of 113 patients with HER3-high or HER3-low, HR-positive/HER2-negative metastatic breast cancer, 53 patients with HER3-high triple-negative breast cancer and 14 patients with HER3-high, HER2-positive metastatic breast cancer was conducted.

Assessing the safety and efficacy of treatment with HER3-DXd was the main goal of the study.

A median of six prior lines of therapy had been administered in the advanced setting to patients with HR-positive/HER2-negative disease before study enrollment. Those with metastatic triple-negative breast cancer received a median of two prior therapies. As for patients with HER2-positive metastatic breast cancer, they received a median of 5.5 prior therapies.

A pooled safety analysis of all 182 patients was conducted. Treatment-emergent side effects led 9.9% of the patients in the study to discontinue treatment.

Treatment-related severe or worse side effects were reported in 120 patients. Some of the side effects included, but were not limited to, decreased appetite, nausea, fatigue, diarrhea and vomiting.

Twelve patients developed treatment-related interstitial lung disease or pneumonitis, which is inflammation of the lungs.

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