Cytogenetic Alterations in Her2/Neu Gene (HER2) and Chromosome 17 (chr17) by Fluorescent In-Situ Hybridization (FISH) in Immunohistochemically (IHC) Equivocal (2+) Breast Cancers.
Dhananjay A Chitale, Jessica Sanchez, Adewale Adeyinka. Henry Ford Hospital, Detroit, MI; Henry Ford Hospital, Detroit
Background: HER2 protein overexpression & gene amplification are prognostic markers for aggressive breast cancers and predictive of response to the trastuzumab, making accurate HER2 status critical. Equivocal HER2IHC results have been recognized as the main source of discrepancy between IHC and FISH results. We sought to determine the frequency of HER2 amplification, intratumoral heterogeneity, HER2 gene duplication, aneuploidy of chr17 and other genetic alterations by FISH in HER2IHC equivocal breast cancers.
Design: We retrieved all cases of breast cancer tested for HER2FISH using commercial 2 color probes [HER2, centromeric enumeration probe (CEP17)] over last 4 years. At least 60 invasive tumor nuclei were analyzed by 2 technologists. Ratio of HER2:CEP17 signals was calculated & scored per CAP/ASCO guidelines (Negative-less than 1.8, equivocal-1.8 to 2.2; positive-over 2.2). >30% nuclei with three or more CEP17 signals irrespective of HER2 copy number were considered to have aneuploidy chr17. Duplication of HER2 gene was defined as 1) ratio>1.3 but <2, 2) <30% of nuclei with 3 or more CEP17, 3) <60% of nuclei with 1 CEP17.
Results: 545/730 cases tested for HER2FISH were equivocal by HER2IHC. 420/545(77.1%) were negative for HER2 amplification, 91/545(16.7%) positive [42(7.7%) high+, 49(9.0%) low+ (ratio 2.2 -3.9)], 34/545(6.2%) equivocal. Significant heterogeneous HER2 signal with duplication/amplification of HER2 gene with/without aneuploidy of chr17 was most frequent in low+ and equivocal HER2FISH [44/545 (8.1%)-28 low +, 13 equivocal, 3 negative]. Duplication of HER2 gene was noted in 29/34(85.3%) of HER2FISH equivocal cases in contrast to 21/49(42.9%) low+ cases. 35/545 tumors revealed abnormality in chr17 [30 polysomy,3 deletion of CEP17, 1 monosomy, 1 amplification of CEP17 with normal HER2].
Conclusions: About 17% of HER2IHC equivocal cases showed HER2 amplification. Heterogeneity of HER2 signal was relatively a low occurrence but was prevalent in low+ cases thus supporting routine HER2FISH testing on biopsies where fixation is better than excisional specimens. Duplication of HER2 gene was more prevalent in HER2FISH equivocal cases. Duplication likely led to increased protein expression of 2+ intensity by IHC. 6.4% of our cases revealed abnormality of chr17 which is thought to be an independent adverse factor in breast cancers. Studies using array comparative genomic hybridization will give further insight into status of gains and loss on entire chr17.
Wednesday, March 2, 2011 9:30 AM
Poster Session V # 5, Wednesday Morning