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Ref Type Journal Article
PMID (33559918)
Authors Mukohara T, Hosono A, Mimaki S, Nakayama A, Kusuhara S, Funasaka C, Nakao T, Fukasawa Y, Kondoh C, Harano K, Naito Y, Matsubara N, Tsuchihara K, Kuwata T
Title Effects of ado-trastuzumab emtansine and fam-trastuzumab deruxtecan on metastatic breast cancer harboring HER2 amplification and the L755S mutation.
Journal The oncologist
Date 2021 Feb 09
Abstract Text Somatic mutations in human epidermal growth factor receptor 2 (HER2) are present in approximately 3% of breast cancers. Some HER2 mutations are activating, and they represent a mechanism of resistance to conventional anti-HER2 therapies such as trastuzumab and lapatinib. Consistently, in patients with HER2-amplified breast cancer, these mutations are predominantly observed in metastatic tumors obtained after exposure to anti-HER2 systemic therapies, possibly after clonal selection. Therefore, it is rare to find co-existent HER2 mutation and amplification in the early clinical course, and thus, the clinical relevance of HER2 mutation to the sensitivity to HER2-targeted drugs, particularly antibody-drug conjugates (ADCs) such as ado-trastuzumab emtansine (T-DM1) and the recently approved fam-trastuzumab deruxtecan (T-DXd), remains unclear. In this study, we described a patient with de novo metastatic breast cancer who exhibited both HER2 amplification and the L755S mutation in the untreated primary breast tumor obtained at the initial diagnosis, and the lesion responded to T-DM1 and T-DXd after exhibiting clinical resistance to other HER2-targeted drugs. Our current case findings suggested that anti-HER2 ADCs should be prioritized over conventional trastuzumab- or lapatinib-based therapies for patients with HER2-amplified and co-mutated tumors. KEY POINTS: Although HER2 mutations were implicated in resistance to anti-HER2 monoclonal antibodies or HER2 TKIs in preclinical studies, their clinical impact on sensitivity to anti-HER2 drugs is unclear owing to the rarity of concomitant HER2 mutation and HER2 amplification. A case of de novo metastatic breast cancer harboring both HER2 amplification and the L755S mutation in an untreated breast primary tumor displayed clinical resistance to standard trastuzumab- or lapatinib-based therapies but good responses to T-DM1 and T-DXd. Anti-HER2 ADCs such as T-DM1 and T-DXd may be prioritized over conventional trastuzumab- or lapatinib-containing therapies for patients with HER2-amplified and co-mutated tumors.


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Molecular Profile Treatment Approach
Gene Name Source Synonyms Protein Domains Gene Description Gene Role
Therapy Name Drugs Efficacy Evidence Clinical Trials
Drug Name Trade Name Synonyms Drug Classes Drug Description
Gene Variant Impact Protein Effect Variant Description Associated with drug Resistance
Molecular Profile Indication/Tumor Type Response Type Therapy Name Approval Status Evidence Type Efficacy Evidence References