Evaluating risk factors for Trastuzumab-Deruxtecan Pneumonitis in patients with metastatic breast cancer.

BACKGROUND

Trastuzumab deruxtecan (T-DXd) is FDA-approved for treatment of patients with HER2 positive and HER2-low metastatic breast cancer. Currently, there is limited understanding of pre-treatment risk factors for pneumonitis associated with T-DXd.

METHODS

Consecutive breast cancer patients who received at least one dose of T-DXd at a single academic cancer study between January 1, 2019, and February 20, 2024, were identified for analysis. Pneumonitis was documented by the treating oncologist at the time of toxicity and retrospectively independently confirmed by a member of the study team through chart and radiologic review. Pre-treatment variables of interest were collected, including patient demographics, radiation dosimetry variables, and chest imaging abnormalities.

RESULTS

Of 179 total patients, 23 (12.8%) had pneumonitis after T-DXd exposure. Patients with pneumonitis had lower baseline oxygen saturation (98% vs. 97%, p = 0.02) and were more likely to have received abemaciclib (26.1% vs. 9.6%, p = 0.03) before T-DXd. Multiple pre-treatment variables were not found to be associated with T-DXd pneumonitis, including chest imaging abnormalities (41.9% vs. 47.8%, p = 0.59), prior immune checkpoint inhibitor treatment (16.0% vs. 8.7%, p = 0.50) and prior chest or breast radiation (61.5% vs. 47.8%, p = 0.20). On multivariate analysis, prior treatment with abemaciclib remained significantly associated with T-DXd pneumonitis (OR 3.25 [1.07-9.11], p = 0.04), while neither pre-treatment chest imaging abnormalities nor prior chest or breast radiation were associated (OR 1.60 [0.62-4.20], p = 0.33); OR 0.51 [0.20-1.33], p = 0.17).

CONCLUSIONS

In this cohort, prior treatment with abemaciclib may be a risk factor for T-DXd pneumonitis. Conversely, pre-treatment chest imaging abnormalities, prior immune checkpoint inhibitor treatment, and prior chest or breast radiation did not increase the risk of T-DXd pneumonitis. Larger studies are warranted to validate these findings toward an improved understanding of risk factors for pneumonitis after T-DXd exposure.