A recent study to determine the impact of revised ASCO/CAP 2013 HER2 guidelines on the clinical practice of pathologists and oncologists, revealed that 2013 guidelines increase the detection of HER2 positive cases, without introducing significant difference in discordance rate of the IHC and FISH assays.
The retrospective analysis was done on 1739 invasive breast carcinoma patients that underwent reflex HER2 (FISH) testing, using both 2007 and 2013 guidelines (2007-2014). Sixty-nine cases equivocal by 2007 guidelines (12% of all equivocal cases) were converted to HER2 positive by 2013 guidelines. Reflex FISH testing of all IHC 1+ cases additionally detected 58 patients (5%; 95% CI 4-6%) with HER2 amplification.
Authors recommend IHC 1+ cases should be offered reflex FISH testing because failure to test them will miss a small number (5%) of potentially treatable cases.
http://www.clinical-breast-cancer.com/article/S1526-8209(16)30360-3/pdf
