SK-OV-3 cells are HER2 gene-amplified25 while MDA-MB-468 cells are not amplified for the HER2 gene, thus the pattern of HER2 heterogeneity in tumors formed of a mixture of SK-OV-3 and MDA-MB-468 cells in our study could be classified as “genetic heterogeneity.” It should be noted that in patients with HER2-positive BC, besides intratumoral HER2 heterogeneity, there may be interlesional HER2 heterogeneity. The gene discussed is ERBB2; the disease is breast cancer.