This approach to HER2-equivocal breast cancers contrasts with our experience using alternative controls.23,24 Based on early studies of control genes on chromosome 172,3,25 and preliminary findings from the Breast Cancer International Research Group/Translational Research in Oncology (BCIRG/TRIO) central laboratories, we hypothesized that use of chromosome 17 p-arm controls to establish HER2 gene status of ISH-equivocal breast cancers could lead to false-positive classifications in a significant proportion of cases. Here, ERBB2 is linked to breast cancer.