ERBB2 and neoplasm: To test whether neighboring chromosomal features or functional elements outside the oncogenes played a role in amplicon formation or tumor growth in multiple samples, we measured the size of the overlap between amplified intervals containing the top three oncogenes—EGFR, MYC, and ERBB2. For each oncogene, and each pair of samples focally amplifying the oncogene, we measured the size of the overlap to evaluate the hypothesis that the size of the overlap was significantly larger than in a null model in which overlaps are obtained from a random choice of breakpoints around the oncogene.