Trastuzumab deruxtecan in HER2-positive advanced gastric cancer: exploratory biomarker analysis of the randomized, phase 2 DESTINY-Gastric01 trial.

Trastuzumab deruxtecan (T-DXd) showed statistically significant clinical improvement in patients with human epidermal growth factor receptor 2-positive (HER2+) gastric cancer in the DESTINY-Gastric01 trial. Exploratory results from DESTINY-Gastric01 suggested a potential benefit in patients with HER2-low gastric cancer. Spatial and temporal heterogeneity in HER2 expression or gene alteration, an inherent characteristic of gastric cancer tumors, presents a challenge in identifying patients who may respond to T-DXd. Specific biomarkers related to therapeutic response have not been explored extensively. Exploratory analyses were conducted to assess baseline HER2-associated biomarkers in circulating tumor DNA and tissue samples, and to investigate mechanisms of resistance to T-DXd. Baseline HER2-associated biomarkers were correlated with objective response rate (ORR) in the primary cohort of patients with HER2+ gastric cancer. The primary cohort had 64% concordance between HER2 positivity and HER2 (ERBB2) plasma gene amplification. Other key driver gene amplifications, specifically MET, EGFR and FGFR2, in circulating tumor DNA were associated with numerically lower ORR. Among 12 patients with HER2 gain-of-function mutations, ORR was 58.3% (7 of 12). ORR was consistent regardless of timing of immunohistochemistry sample collection. Further investigations are required in larger studies.

Trastuzumab Deruxtecan in Anti-Human Epidermal Growth Factor Receptor 2 Treatment-Naive Patients With Human Epidermal Growth Factor Receptor 2-Low Gastric or Gastroesophageal Junction Adenocarcinoma: Exploratory Cohort Results in a Phase II Trial.

PURPOSE: To investigate efficacy and safety of trastuzumab deruxtecan (T-DXd) in human epidermal growth factor receptor 2 (HER2)-low gastric or gastroesophageal junction (GEJ) adenocarcinoma. METHODS: Patients with locally advanced or metastatic HER2-low (cohort 1, immunohistochemistry 2+/in situ hybridization-negative; cohort 2, immunohistochemistry 1+) gastric/GEJ adenocarcinoma treated with at least two prior regimens, including fluoropyrimidine and platinum, but anti-HER2 therapy naive, received T-DXd 6.4 mg/kg intravenously once every 3 weeks. The primary end point was confirmed objective response rate by independent central review. RESULTS: Among 21 patients enrolled in cohort 1 and 24 enrolled in cohort 2, 19 and 21 patients, respectively, had central HER2 confirmation, received T-DXd, and had measurable tumors at baseline. The confirmed objective response rate was 26.3% (95% CI, 9.1 to 51.2) from five partial responses in cohort 1 and 9.5% (95% CI, 1.2 to 30.4) from two partial responses in cohort 2. Thirteen patients (68.4%) in cohort 1 and 12 (60.0%) in cohort 2 experienced reduced tumor size. The median overall survival was 7.8 months (95% CI, 4.7 to nonevaluable) in cohort 1 and 8.5 months (95% CI, 4.3 to 10.9) in cohort 2; the median progression-free survival was 4.4 months (95% CI, 2.7 to 7.1) and 2.8 months (95% CI, 1.5 to 4.3), respectively. The most common grade ≥ 3 treatment-emergent adverse events in cohorts 1 and 2 were anemia (30.0% and 29.2%), decreased neutrophil count (25.0% and 29.2%), and decreased appetite (20.0% and 20.8%). Drug-related interstitial lung disease/pneumonitis occurred in one patient in each cohort (grade 1 or 2). No drug-related deaths occurred. CONCLUSION: This study provides preliminary evidence that T-DXd has clinical activity in patients with heavily pretreated HER2-low gastric/GEJ adenocarcinoma.

Trastuzumab Deruxtecan in Previously Treated HER2-Positive Gastric Cancer.

BACKGROUND: Trastuzumab deruxtecan (DS-8201) is an antibody-drug conjugate consisting of an anti-HER2 (human epidermal growth factor receptor 2) antibody, a cleavable tetrapeptide-based linker, and a cytotoxic topoisomerase I inhibitor. The drug may have efficacy in patients with HER2-positive advanced gastric cancer. METHODS: In an open-label, randomized, phase 2 trial, we evaluated trastuzumab deruxtecan as compared with chemotherapy in patients with HER2-positive advanced gastric cancer. Patients with centrally confirmed HER2-positive gastric or gastroesophageal junction adenocarcinoma that had progressed while they were receiving at least two previous therapies, including trastuzumab, were randomly assigned in a 2:1 ratio to receive trastuzumab deruxtecan (6.4 mg per kilogram of body weight every 3 weeks) or physician's choice of chemotherapy. The primary end point was the objective response, according to independent central review. Secondary end points included overall survival, response duration, progression-free survival, confirmed response (response persisting ≥4 weeks), and safety. RESULTS: Of 187 treated patients, 125 received trastuzumab deruxtecan and 62 chemotherapy (55 received irinotecan and 7 paclitaxel). An objective response was reported in 51% of the patients in the trastuzumab deruxtecan group, as compared with 14% of those in the physician's choice group (P<0.001). Overall survival was longer with trastuzumab deruxtecan than with chemotherapy (median, 12.5 vs. 8.4 months; hazard ratio for death, 0.59; 95% confidence interval, 0.39 to 0.88; P = 0.01, which crossed the prespecified O'Brien-Fleming boundary [0.0202 on the basis of number of deaths]). The most common adverse events of grade 3 or higher were a decreased neutrophil count (in 51% of the trastuzumab deruxtecan group and 24% of the physician's choice group), anemia (38% and 23%, respectively), and decreased white-cell count (21% and 11%). A total of 12 patients had trastuzumab deruxtecan-related interstitial lung disease or pneumonitis (grade 1 or 2 in 9 patients and grade 3 or 4 in 3), as adjudicated by an independent committee. One drug-related death (due to pneumonia) was noted in the trastuzumab deruxtecan group; no drug-related deaths occurred in the physician's choice group. CONCLUSIONS: Therapy with trastuzumab deruxtecan led to significant improvements in response and overall survival, as compared with standard therapies, among patients with HER2-positive gastric cancer. Myelosuppression and interstitial lung disease were the notable toxic effects. (Funded by Daiichi Sankyo; DESTINY-Gastric01 ClinicalTrials.gov number, NCT03329690.).