FDA labeling for trastuzumab deruxtecan states that this agent should be discontinued permanently in patients who develop symptomatic interstitial lung disease or pneumonitis (grade 2 or higher). The FDA recommends managing grade 3 neutropenia with treatment interruption, followed by reinstatement at the full recommended starting dose of 5.4 mg/kg. Neither grade 2 diarrhea nor grade 3 anemia would be considered reasons for immediate permanent discontinuation of this therapy.

Reference:
ENHERTU® (fam-trastuzumab deruxtecan-nxki). Prescribing information. Daiichi Sankyo, Inc.; November 2022.