We used digital arrays to analyze the ERBB2 copy numbers of 40 breast cancer and 8 normal breast tissue DNA samples from BioChain (Hayward, CA). All DNA samples were from Asian individuals except one normal sample that was from a Caucasian. Of the 40 breast cancer samples, 3 are adenocarcinoma, 1 is fibroadenoma, 2 are invasive lobular carcinoma, 1 is infiltrative ductal carcinoma and 33 are invasive ductal carcinoma. The samples were STA-treated and, for screening purpose, the products were analyzed using only two panels for each sample on digital arrays. The results are shown in Figure 5 . Fourteen breast cancer samples (35%) had a diploid ERBB2 copy number of more than five while all control samples were below five copies [an absolute number of ERBB2 copies greater than 4.0 per cell is considered amplification in FISH analysis (47) . Here we use five as the threshold]. The copy numbers shown are not all integers due to (i) heterogeneity of the cancer cells and (ii) sampling variations as only two panels were used for each sample.