ERBB2 and neoplasm: In the remaining 22 cases, the HercepTest (mAb) stained at least some tumor cells, with approximately one-third of these cases belonging to the HER2-low group (7 × IHC 1 + , 1 × IHC 2 + non-amplified) and 14 cases in the HER2 “ultra-low” group with < 10% stained tumor cells (see also Fig. 3B, marked in grey), thus highlighting the high sensitivity of the HercepTest (mAb) used in this study.