HER2 FISH confirmed the HER2 amplification (Fig. 2D) in this specimen as a group 1 positive HER2 FISH result per 2018 ASCO/CAP breast cancer guideline for dual color probes when the HER2/CEP17 ratio is ≥ 2 and the average HER2 copy number is ≥ 4.0 signals per cell [23]. Here, ERBB2 is linked to breast cancer.