**3.2 HER2-enriched subtype**

The HER2-enriched subtype (previously the HER2+/ER- subtype) is characterized by high expression of the HER2 and proliferation gene clusters, and low expression of the luminal cluster. For this reason, these tumors are typically negative for ER and PR, and positive for HER2. It is important to note that this subtype comprises only about half of clinically HER2 positive breast cancer. The rest have high expression of both the HER2 and luminal gene clusters and fall in a luminal subtype. Promotion in HER2-directed therapy has improved the poor prognosis of this subtype.
