ERBB2 and cancer: The p-arm alternative control loci had a significantly higher rate of deletions relative to q-arm loci (eTable 1 in the Supplement)(P < .001) with SMS the most frequently lost, followed by D17S122 and TP53. The frequency of q-arm heterozygous deletions among HER2-equivocal cancers was low, with only TOP2A reaching 8%.