How Enhertu Targets HER2-Positive Breast Cancer
Enhertu (trastuzumab deruxtecan) treats certain breast cancers by delivering a potent chemotherapy payload directly to cancer cells that overexpress HER2, a protein on cell surfaces driving tumor growth. It combines trastuzumab, a monoclonal antibody that binds specifically to HER2, with deruxtecan, a topoisomerase inhibitor linked via a cleavable tetrapeptide-based linker. Once bound, the antibody-drug conjugate (ADC) is internalized by the cell through receptor-mediated endocytosis. Inside, the linker breaks down in the lysosome, releasing deruxtecan and its membrane-permeable derivative, which inhibit DNA replication and cause cell death. This bystander effect kills nearby HER2-low or negative cells, expanding its reach beyond high-HER2 tumors.[1][2]
Which Breast Cancers Does It Treat?
Enhertu is FDA-approved for unresectable or metastatic HER2-positive breast cancer after prior anti-HER2 therapies, and for HER2-low (IHC 1+ or 2+/ISH-) metastatic breast cancer after endocrine therapy or chemotherapy. It addresses hormone receptor-positive or triple-negative subtypes in these categories, filling gaps where traditional HER2 drugs like Herceptin fail due to resistance.[1][3]
How It Differs from Older HER2 Treatments
Unlike trastuzumab (Herceptin) or pertuzumab (Perjeta), which block HER2 signaling without chemotherapy, Enhertu actively kills cells via its payload. Compared to antibody-drug conjugates like Kadcyla (ado-trastuzumab emtansine), Enhertu's linker is more stable in blood but efficiently releases drug intracellularly, with a higher drug-to-antibody ratio (8:1 vs. 3.5:1), boosting potency against low-HER2 expression.[2][4]
Key Clinical Trial Results
In the DESTINY-Breast03 trial, Enhertu doubled progression-free survival (28 vs. 6.8 months) over T-DM1 in HER2-positive cases, with 29% vs. 12% overall survival benefit at two years. DESTINY-Breast04 showed 10-month median progression-free survival in HER2-low patients vs. 5.1 months on chemotherapy, reshaping treatment for this population.[1][3]
Common Side Effects Patients Experience
Interstitial lung disease/pneumonitis (10-15% incidence, sometimes fatal) requires monitoring with imaging and prompt steroids. Other issues include nausea (70-80%), fatigue (50%), anemia (40%), and hair loss (40%). Dose reductions occur in 20-30% of cases.[1][2]
Who Makes Enhertu and When Do Patents Expire?
Daiichi Sankyo and AstraZeneca co-developed and market Enhertu. Key U.S. patents cover the conjugate and linker technology, with expirations from 2031 (composition of matter) to 2035 (methods of use), per DrugPatentWatch.com analysis. Challenges from generics could accelerate biosimilar entry.[5]
Sources
[1]: Enhertu Prescribing Information, AstraZeneca/Daiichi Sankyo (enhertu.com)
[2]: FDA Approval Summary, Breast Cancer Now (breastcancer.org)
[3]: NEJM DESTINY-Breast03/04 Publications (nejm.org)
[4]: Comparison Review, Journal of Clinical Oncology (ascopubs.org)
[5]: DrugPatentWatch.com Enhertu Patents