Among 100 ASCO-CAP FISH group 4 (HER2-equivocal) breast cancers, we identified heterozygous deletions (Table 2) (eTable 1 and eFigure 2 in the Supplement) in 65 for the SMS locus, 46 for D17S122, 43 for TP53, 8 for TOP2A, none for RARA, and none for HER2 (eTable 1 in the Supplement). The gene discussed is ERBB2; the disease is breast carcinoma.