Trastuzumab Deruxtecan with Nivolumab in HER2-Expressing Metastatic Breast or Urothelial Cancer: Analysis of the Phase Ib DS8201-A-U105 Study

PURPOSE: This multicenter phase Ib study investigated trastuzumab deruxtecan (T-DXd) plus nivolumab in patients with HER2-expressing metastatic breast cancer (mBC) and metastatic urothelial cancer (mUC). PATIENTS AND METHODS: Part 1 determined the recommended dose for expansion of T-DXd plus nivolumab. Part 2 evaluated efficacy and safety; the primary endpoint was confirmed objective response rate by independent central review. RESULTS: In part 1, seven patients with mBC were enrolled and received T-DXd 3.2 mg/kg (four patients) or 5.4 mg/kg (three patients) plus nivolumab. The recommended dose for expansion for T-DXd was 5.4 mg/kg plus nivolumab 360 mg intravenously every 3 weeks. In part 2, 32 patients with HER2-positive mBC (cohort 1; inclusive of three administered 5.4 mg/kg in part 1), 16 with HER2-low mBC (cohort 2), 30 with HER2-high mUC (cohort 3), and four with HER2-low mUC (cohort 4) were enrolled. At data cutoff (July 22, 2021), the confirmed objective response rates (95% confidence interval) for cohorts 1 to 4 were 65.6% (46.8%-81.4%), 50.0% (24.7%-75.3%), 36.7% (19.9%-56.1%), and not assessed due to small sample size, respectively. The median treatment duration (range) with T-DXd in cohorts 1 to 4 was 8.9 (1-23) months, 6.9 (1-21) months, 3.9 (1-21) months, and not assessed, respectively; the most common treatment-emergent adverse event was nausea (55.2%, 62.5%, 73.3%, and 75.0%, respectively). Adjudicated drug-related interstitial lung disease/pneumonitis rates (cohorts 1-3) were 20.7%, 0%, and 20.0%, respectively (one grade 5 each, cohorts 1 and 3). CONCLUSIONS: T-DXd plus nivolumab demonstrated promising antitumor activity in HER2-expressing mBC or mUC and safety consistent with the known profile of T-DXd. Interstitial lung disease/pneumonitis is an important risk and requires careful monitoring and prompt intervention.