HER2 FISH results in breast cancers with increased CEN17 signals using alternative chromosome 17 probes - reclassifying cases in the equivocal category.

An increased cen17 copy number does not necessarily reflect polysomy, and reflex testing facilitates the reclassification of 'equivocals'. Nevertheless, the prognostic and predictive value of a HER2/cen17 co-amplification versus HER2 gene amplification alone must still be evaluated prospectively.