MKI67 and breast cancer: Though treated in the same manner as patients with HER2 IHC 0+ BC, patients with HER2-low breast cancer may portray a clinical picture closer to that of HER2-positive BC patients: in a large prospective series, patients with HER2 IHC 2+, FISH-negative BC tended to present with larger tumor size, higher histopathological grade, higher Ki67, and more frequently with axillary nodal involvement [19].