| Abstrakt: |
Objectives: The 2013 ASCO-CAP HER2 guidelines recommend testing all invasive breast cancers for HER2, typically with IHC followed by ISH when IHC is equivocal (2+). As welldifferentiated breast cancers are rarely HER2 positive, we questioned the value of performing routine reflex HER2 ISH testing in this subset of breast cancers. Methods: We collected all HER2 IHC equivocal cases with subsequent FISH data from primary breast cancers with well-differentiated tumour types at our centre from 2010 to 2015. H&E and IHC slides were reviewed to confirm tumour type, grade, and IHC score. Results: Three of 92 cases (3.3%) were positive for HER2 amplification, one of which had chromosome 17 monosomy. The mean HER2 count and HER2:CEP17 ratio for these cases was 4.6 and 2.54 respectively. One amplified case was invasive lobular carcinoma, grade 2, and two were invasive ductal carcinomas, grade 1. Cold ischemic time was prolonged in two of the amplified cases, one of which was rescored as 1+ upon review of the IHC. Basolateral staining was noted in one amplified case and in 26/84 (31%) non-amplified cases. This predominantly incomplete membranous staining pattern was also observed in 9/19 cases of invasive ductal carcinoma that were rescored as 1+ by the recently published modification of the 2013 guidelines. Conclusions: Given the low rate of HER2 amplification in well-differentiated breast cancers, consideration could be given to performing reflex ISH testing for IHC 2+ cases with adverse prognostic factors, non-optimal preanalytical conditions, or upon clinician request. [ABSTRACT FROM AUTHOR] |
