Maintenance Treatment After Enhertu in HER2+ Breast Cancer
Continue Enhertu (trastuzumab deruxtecan) until disease progression or unacceptable toxicity—there is no separate "maintenance therapy" after Enhertu in HER2+ breast cancer. Enhertu itself is the treatment, not a bridge to maintenance.
Understanding the Treatment Paradigm
The concept of "maintenance therapy" after Enhertu reflects a misunderstanding of how antibody-drug conjugates (ADCs) work compared to traditional chemotherapy regimens. Unlike older HER2-targeted therapy combinations where chemotherapy is stopped after 4-6 months and only the HER2-targeted agent continues 1, Enhertu is both the HER2-targeted therapy AND the cytotoxic payload in one molecule. You cannot separate them.
What the Guidelines Actually Say
The ASCO guidelines 1 clearly state that when patients receive HER2-targeted therapy plus chemotherapy combinations, the chemotherapy continues for approximately 4-6 months, then clinicians should "continue the HER2-targeted therapy; no further change in the regimen is needed until the time of progression or unacceptable toxicities." However, these recommendations were written before Enhertu's approval and apply to regimens like trastuzumab-pertuzumab-taxane, not to ADCs.
The 2022 ASCO update 2 now recommends Enhertu as preferred second-line therapy after progression on first-line trastuzumab-pertuzumab-taxane. The 2025 expert recommendations 3 confirm Enhertu as the standard second-line treatment (ESMO-MCBS 1A).
The Correct Approach
Continue Enhertu at 5.4 mg/kg IV every 3 weeks until:
- Disease progression (by imaging or clinical assessment)
- Unacceptable toxicity (particularly interstitial lung disease, neutropenia, or left ventricular dysfunction) 4
- Patient decision to discontinue
Key Monitoring Requirements
While on Enhertu, you must monitor for:
Interstitial Lung Disease (ILD): The most critical toxicity, occurring in 12% of patients with median onset at 5.5 months 4. Permanently discontinue for Grade ≥2 symptomatic ILD. For Grade 1 asymptomatic ILD, hold Enhertu and consider corticosteroids (≥0.5 mg/kg/day prednisolone).
Neutropenia: Check CBC before each dose. Sixty-five percent of patients experience decreased neutrophil counts 4. Dose reduce or hold based on severity.
Cardiac Function: Assess LVEF before starting and regularly during treatment. Permanently discontinue if LVEF <40% or absolute decrease >20% from baseline 4.
What Happens After Enhertu Progression?
This is the actual question you should be asking. Real-world data shows limited options with modest efficacy:
Post-Enhertu Treatment Options:
The EN-SEMBLE study 5 of 664 patients showed median progression-free survival after Enhertu was only 4.1 months (95% CI 3.9-4.5), with median overall survival of 16.2 months. Treatment options included:
- Anti-HER2 antibodies (trastuzumab-based regimens): Used in 361/664 patients
- HER2 tyrosine kinase inhibitors (tucatinib, lapatinib, neratinib): Used in 113/664 patients
- Other chemotherapy regimens
Regimens containing trastuzumab showed numerically longer time-to-treatment-failure than TKIs alone 6, though differences were not statistically significant. The 2025 expert recommendations 3 suggest tucatinib plus trastuzumab plus capecitabine as a third-line option after Enhertu progression.
Special Consideration: ILD History
If a patient developed ILD during Enhertu treatment, the recurrence/exacerbation rate with subsequent therapy was only 3.2% 5. Patients who discontinued Enhertu due to adverse events (including ILD) actually had numerically longer survival with subsequent treatments 5, likely reflecting better performance status and less aggressive disease biology.
Hormone Receptor-Positive Disease
For patients with HR+/HER2+ disease who achieve response or stable disease on Enhertu, you may consider adding endocrine therapy to Enhertu based on the ASCO guideline principle that endocrine therapy can be added to HER2-targeted therapy when chemotherapy ends 1. However, this is informal consensus with insufficient evidence (weak recommendation). The primary strategy remains continuing Enhertu alone until progression.
Common Pitfall to Avoid
Do not stop Enhertu at an arbitrary timepoint (like 6 months) expecting to transition to "maintenance." This is not supported by any guideline or the drug label. Enhertu demonstrated superior efficacy in DESTINY-Breast03 precisely because it was continued until progression 3. Stopping prematurely abandons effective therapy without evidence of benefit.