ERBB2 and neoplasm: On average, the mean local diversity was higher in the case of HER2 than for ER (mean = 0.85 vs. 0.69, Supplementary Figure 6C and 6D), but interestingly the ER local diversity index was significantly more variable from region to region of the same tumor (mean coefficient of variation = 0.2 for ER vs. 0.08 for HER2, Mann-Whitney test, P < 0.0001, Figure 5A), possibly reflecting differences in the mutational or dispersal rates of different sub-clones expressing various levels of HER2 and ER.