About HER2-low mBC

Historically, HER2 status has been viewed in binary terms: positive or negative1

Until now, ~85% of patients with BC were classified as HER2-negative and were not eligible for anti-HER2 therapy1

Of the approximately 85% of patients with breast cancer who are deemed HER2-negative, 60% have low 
levels of HER2 expression (IHC 1+ or IHC 2+/ISH–) Of the approximately 85% of patients with breast cancer who are deemed HER2-negative, 60% have low 
levels of HER2 expression (IHC 1+ or IHC 2+/ISH–)

Low HER2 expression occurs in both HR+ and HR– mBC, and has previously not been actionable3

HR positive

For patients classified with HR+/HER2-negative mBC, outcomes decline once endocrine therapy (ET) has been exhausted4-6

  • mPFS decreases from ~16-28 months with ET-based options to ~5 months with subsequent chemotherapya
HR negative

For patients classified with HR–/HER2-negative mBC who are ineligible for or have exhausted targeted treatment, chemotherapy remains the only option7,8

  • mPFS decreases from ~10 months with first-line options to ~2 months with subsequent chemotherapya

amPFS ranges represent estimates from publicly available clinical trial data. These clinical trials were conducted independently, and their outcomes are not intended to be used as a cross-trial comparison.

The treatment landscape is evolving, and the need to identify additional targetable
populations, including patients with HER2-low mBC, has become critical1

BC, breast cancer; HER2, human epidermal growth factor receptor 2; HR+, hormone receptor-positive; HR–, hormone receptor-negative; IHC, immunohistochemistry; ISH, in situ hybridization; mBC, metastatic breast cancer; mPFS, median progression-free survival.

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