Impact of 2013 ASCO/CAP guidelines on HER2 determination of invasive breast cancer: A single institution experience using frontline dual-color FISH.

1028Background: ASCO/CAP new guidelines published in 2013 (AC2013) significantly modified the scoring criteria for HER2-FISH. We retrospectively evaluated the impact of AC2013 in a five-year cohort of consecutive invasive breast cancers (IBCs) underwent frontline dual-color FISH. Furthermore, we applied three different reflex tests and investigated clinical outcomes of patients with HER2-equivocal IBC. Methods: 2788 consecutive IBCs that underwent frontline HER2/CEP17 determination in our institution from January 2009 to December 2013 were reclassified based on the AC2013 guidelines. FISH HER2-equivocal cases underwent reflex tests: HER2-IHC, RARA-FISH, and SMS-FISH. Clinico-pathological correlation was performed. Results: Two hundred HER2-negative cases (7.2%) were classified differently based on the AC2013: 0.3% (8/2788) became HER2-positive and 6.9% (192/2788) HER2-equivocal. AC2013 equivocal-IBCs represented a subgroup of grade 3, luminal-like subtype IBCs, in patients with a higher age. After reflex ...