To date, there are several biological characteristics implicated in response to anti-HER2 therapy, including the hormone receptor status [18–20], intrinsic subtype [21], immune signatures [22], tumour-infiltrating lymphocytes (TILs) [23], and alterations in signalling pathways downstream of the ErbB2 family (e.g., PI3K/Akt activation) [24–26]. The gene discussed is PIK3CA; the disease is neoplasm.