If there is HER2-low discordance between primary and subsequent breast cancer biopsies, in which scenarios would you choose to use trastuzumab deruxtecan?
If there is discordance in HER2 IHC between between primary and metastatic site, would you still use T-Dxd for HER2-low breast cancer?
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Because of the potential heterogeneity of HER2 expression, I would still offer T-DXd for these patients. In addition, HER2 IHC 0 may not exclude T-DXd activity based on the DAISY trial.
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Discordance in HER2 receptor status between primary and metastatic deposits can occur in up to 1/3 of samples. As with hormone receptor status, specimens collected via fine needle aspirate or on decalcified bone may produce inconsistent results for HER2 IHC.
I always recommend biopsy of a metastatic...
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In patients with Her-low disease (IHC 1+ or 2 + with negative Her 2 FISH), I would favor obtaining new tissue from recurrent or metastatic site before considering drugs like Trastuzumab deruxtecan. Repeat biopsy will not only help verify the contemporary Her 2 status, but also allow testing for othe...
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Yes, if metastatic disease is HER2 low.
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