Importantly, dual-probe ISH methods ascertain CN of the chromosome 17 centromere and therefore can distinguish monosomy vs polysomy/co-amplification, revealing five possible test result scenarios: 95% fall into either group 1 classic HER2 amplified or group 5 classic HER2 non-amplified cancer, and the remaining 5% fall into either group 2 monosomy 17, group 3 co-amplification/polysomy 17, or group 4 borderline/equivocal13. The gene discussed is ERBB2; the disease is cancer.