| Consensus Statement | Quality of Evidence | Strength of Rec. | Key Ref |
|---|---|---|---|
| 1. For PIK3CA gene, both somatic tissue and liquid biopsy testing can be used for determining mutation status. | I | A | 1-3 |
| 2. Mutations in somatic PIK3CA/AKT1/PTEN, ESR1, and germline pathogenic BRCA1/2 mutations are associated with improved treatment outcome to relevant targeted therapies. | I | A | 1-5 |
| 3. In HR(+) mBC with HER2-low (IHC 1+ or IHC 2+/ISH-), HER2-ultralow (IHC 0 with membrane staining) is predictive of trastuzumab deruxtecan treatment efficacy. | I | A | 6-7 |
| 4. ESR1 mutation, determined by circulating tumor DNA has both predictive and prognostic indicator values. | I | A | 4,5,8 |
| 5. Determination of TROP2 expression status is not required for decision of TROP2 antibody drug conjugates use (such as sacituzumab govitecan, datopotamab deruxtecan). | II | B | 8 |
| 6. There is data to support replacing AI with a SERD (e.g. camizestrant) in combination to first line CDK4/6 inhibitor use upon emergence of mutant ESR1 ctDNA before clinical progression # | I | A | 9 |
| 7. Biopsy of metastatic sites may be considered for guiding treatment options if no risk of major complications. | II | A | 10 |
# testing for ESR1 ctDNA started at least 6 months after initiation of CDK4/6 inhibitors plus aromatase inhibitors
References
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