Demonstrating similarly high reproducibility across repeat analyses on independent dates/operators of the well-characterized ERBB2-amplified SK-BR-3 breast cancer cell line, the mean CEP17 CN by ddPCR was 3.03 (SD 0.07) showing gain of one copy, the mean ERBB2 CN was 19.83 (SD 0.42), and the mean ERBB2/CEP17 ratio was 6.55 (SD 0.13). Here, ERBB2 is linked to breast cancer.