Second-Line (2L) Options for HER2-Low Disease

The patient receives 1L treatment with carboplatin plus paclitaxel for mTNBC with visceral crisis. After 3 months, she remains symptomatic with intermittent SBOs. Imaging indicates progressive disease with new hepatic metastases. Biopsy is consistent with prior assessment and shows HR– (ER and PR <1%), HER2– (IHC2+/ISH–) disease.

T-DXd and SG are both antibody-drug conjugates (ADCs) recommended in the 2L setting for mTNBC. T-DXd targets HER2, which is expressed at low levels in ~40% of HR+/HER2–  cases and 23% of TNBC. HER2-low disease is defined as HER2 IHC1+ or IHC2+/ISH–.