Trastuzumab deruxtecan (TDXD) and datopotamab deruxtecan (Dato-DXd) share the same cytotoxic payload, yet Dato-DXd has a much lower rate of interstitial lung disease (ILD). This indicates the toxicity is driven by the antibody-antigen interaction, not the payload itself.

A practice gap exists in managing side effects of Trastuzumab-Deruxtecan (TDXD) between specialties. Breast oncologists, with more experience, are far more aggressive with prophylactic anti-emetics and frequent imaging to detect asymptomatic ILD. This proactive approach is a key lesson for lung cancer specialists and others now adopting the drug.

Unlike many targeted therapies, resistance to the antibody-drug conjugate Trastuzumab-Deruxtecan (TDXD) in HER2-mutant lung cancer is not caused by new HER2 mutations. Instead, resistance mechanisms are linked to the chemotherapy payload, such as the development of efflux pumps, which is a fundamentally different challenge for subsequent treatment strategies.

In the REJOYCE ovarian-1 trial for RDXD, the 5.6 mg/kg dose was selected to move forward over a 6.4 mg/kg dose that showed a higher response rate (57%). The lower dose had significantly fewer serious adverse events and a lower rate of interstitial lung disease (ILD), demonstrating a crucial trade-off where safety and tolerability outweigh peak efficacy in late-stage development.

Despite label warnings against rechallenging trastuzumab deruxtecan (TDXD) after any symptomatic (Grade 2+) interstitial lung disease (ILD), some experts differentiate. For 'soft call' cases with minimal symptoms, they may consider restarting after a transparent patient discussion, believing not all Grade 2 ILDs carry the same risk.

Interstitial lung disease (ILD) is a serious risk with trastuzumab deruxtecan (TDXD). Oncologists must take it extremely seriously, engaging a pulmonologist immediately at the first sign of symptoms or CT scan findings. A collaborative, multidisciplinary approach is essential for safely managing this potentially fatal toxicity.

Contrary to initial fears, both clinical trial and real-world data show that patients experiencing asymptomatic, grade 1 interstitial lung disease (ILD) from TDXD can be safely retreated. This allows patients to continue benefiting from a highly effective therapy without undue risk.

The risk of serious interstitial lung disease (ILD) with the drug TDXD is heavily dependent on the total duration of therapy. A short, 4-cycle neoadjuvant course has a low 4% ILD rate, whereas a longer 14-cycle adjuvant course sees this risk more than double to over 10%, making the shorter pre-surgical approach significantly safer.

Clinicians can confidently reduce the dose of Datopotamab-deruxtecan to manage toxicity. Phase 1 data demonstrates a compelling efficacy signal even at a 4 mg/kg dose level, reassuring oncologists that dose reduction is a viable strategy to maintain treatment without sacrificing benefit.