Among 100 ASCO-CAP FISH group 5 (HER2-not-amplified or ISH-negative) breast cancers, we identified heterozygous deletions in 35 cases for D17S122, 30 for SMS, 3 for TOP2A, 1 for RARA, and none for TP53 (eTable 1 in the Supplement). Here, TOP2A is linked to breast cancer.