Abstract PO5-12-12: Implementation of a comprehensive monitoring protocol for the prevention and treatment of interstitial lung disease in patients undergoing treatment with trastuzumab deruxtecan

Abstract Background: In the DESTINY-BREAST studies, Trastuzumab deruxtecan (T-DXd) demonstrated significant antitumor activity in heavily pretreated patients (pts) with HER2-positive and HER2-low advanced breast cancer (ABC). T-DXd is associated with an increased risk of interstitial lung disease (ILD), which occurs in 10-15% of patients with a 2.2% rate of fatal events. Increased monitoring for ILD within DESTINY-BREAST03 showed a reduction in grade 3-5 events. Patients with a history of clinically significant lung disease were excluded from this study, however this may not be reflective of the standard community patient population treated with T-DXd. There are currently no standardized monitoring protocols for ILD/pneumonitis for pts treated with T-DXd. We conducted a retrospective chart review to assess the benefit of implementing an ILD monitoring protocol in a cohort of patients receiving treatment with T-DXd at the Duke Cancer Institute. Methods: Patients with HER2-positive or HER2-low ABC who received ≥ five cycles of T-DXd between Jan 1, 2020- April 30, 2022 were included. Imaging with CT chest ILD protocol and pulmonary function testing with diffusing capacity for carbon monoxide (DLCO) were performed at baseline prior to initiation of T-DXd, prior to cycle 3 and cycle 5 in conjunction with ILD chest CT and then every 6 weeks to monitor for ILD. DLCO was corrected for hemoglobin. Clinical symptoms including cough, shortness of breath, dyspnea, and new or worsening respiratory symptoms were recorded. For pts that experienced more than a 10% decrease in corrected DLCO (DLCOc), a pulmonology consult was recommended. DLCOc was reviewed in combination with chest imaging and clinical history to evaluate for ILD and guidance was provided for continuation or cessation of T-DXd. Results: A total of 33 patients with HER2-positive (N=27) and HER2-low (N=6) ABC were monitored as per the predefined ILD monitoring protocol. There were 5 confirmed cases of ILD/pneumonitis within the pt cohort. 16 patients (48%) experienced DLCOc decreases >10% warranting a pulmonology consult or further review. Upon further assessment, ILD/pneumonitis was ruled out based on chest imaging and/or asymptomatic presentation in 11 patients and therapy continued without treatment delay or discontinuation. There were 5 confirmed cases of ILD/pneumonitis within the patient cohort. 3 of the 5 patients diagnosed with ILD experienced DLCOc decreases ≥10%, while 2 of the 5 diagnosed patients had DLCOc changes of < 10% but had concern for ILD on ILD/chest CT and were diagnosed after pulmonology consult. Additional results to be presented at meeting. Conclusion: For patients receiving T-DXd, implementation of a comprehensive protocol to monitor and assess for ILD secondary to treatment may allow patients with suspected ILD to begin treatment sooner or prevent permanent discontinuation by excluding ILD diagnosis. While PFT monitoring can be helpful for some patients to monitor for ILD, continuous PFT monitoring is not recommended for all patients given inconsistency. However, baseline PFTs prior to initiation and with suspected ILD in combination with imaging warrants further investigation. The use of a multidisciplinary team including pulmonologists experienced with T-DXd-induced ILD may assist in diagnosing or excluding ILD and allow for continuation of T-DXd therapy. Citation Format: Heather Moore, Kelly Westbrook, Thomas Bagwell, Scott Shofer, Carey Anders, Amy Guisinger, Olivia White, Susan Dent. Implementation of a comprehensive monitoring protocol for the prevention and treatment of interstitial lung disease in patients undergoing treatment with trastuzumab deruxtecan [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO5-12-12.