Background: According to 2018 ASCO/CAP guideline, HER2 FISH-equivocal breast cancers will be categorized as HER2 negative except those with HER2 IHC 3+. However, whether or not HER2 FISH-equivocal breast cancers was a heterogeneous group has not been well illustrated.
Methods: 195 HER2 FISH-equivocal breast cancers were collected between 2014 and 2018. The molecular subtype was determined according to 2013 St Gallen consensus, and HER2 status was also redefined following 2018 ASCO/CAP guideline. All cases were classified into 4 groups according to the average HER2 copy number (4.0-4.4, 4.5-4.9, 5.0-5.4, 5.5-5.9 signals/cell). The relationship between HER2 copy number and clinicopathological parameters was analyzed.
Results: 183 (93.8%) of 195 FISH-equivocal cases were of luminal subtype, while the other 12 (6.2%) were undetermined. Using 2018 ASCO/CAP guideline, all FISH-equivocal cases were recategorized to HER2 negative. Therefore, 31(15.9%) cases were luminal A-like, 152 (77.9%) were luminal B-like (HER2 negative) and 12 (6.2%) were triple negative. The average HER2 copy number showed positive correlation with chromosome 17 polysomy, but had no significant association with other clinicopathological parameters as well as prognosis. 17 (8.7%) cases were treated with trastuzumab, but showed no difference in prognosis with patients who didn’t receive targeted therapy.
Conclusions: In this study, all HER2 FISH-equivocal breast cancers were reclassified to be HER2 negative according to 2018 ASCO/CAP guideline. Most of these patients were luminal B-like (HER2 negative). The average HER2 copy number had no significant association with clinicopathological parameters, as well as prognosis.

Figure 1
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Posted 19 Feb, 2021
On 09 Sep, 2021
Received 03 Sep, 2021
On 30 Aug, 2021
On 29 Aug, 2021
Received 29 Aug, 2021
Received 17 Apr, 2021
On 10 Apr, 2021
Invitations sent on 06 Apr, 2021
On 06 Feb, 2021
On 06 Feb, 2021
On 06 Feb, 2021
On 06 Feb, 2021
Posted 19 Feb, 2021
On 09 Sep, 2021
Received 03 Sep, 2021
On 30 Aug, 2021
On 29 Aug, 2021
Received 29 Aug, 2021
Received 17 Apr, 2021
On 10 Apr, 2021
Invitations sent on 06 Apr, 2021
On 06 Feb, 2021
On 06 Feb, 2021
On 06 Feb, 2021
On 06 Feb, 2021
Background: According to 2018 ASCO/CAP guideline, HER2 FISH-equivocal breast cancers will be categorized as HER2 negative except those with HER2 IHC 3+. However, whether or not HER2 FISH-equivocal breast cancers was a heterogeneous group has not been well illustrated.
Methods: 195 HER2 FISH-equivocal breast cancers were collected between 2014 and 2018. The molecular subtype was determined according to 2013 St Gallen consensus, and HER2 status was also redefined following 2018 ASCO/CAP guideline. All cases were classified into 4 groups according to the average HER2 copy number (4.0-4.4, 4.5-4.9, 5.0-5.4, 5.5-5.9 signals/cell). The relationship between HER2 copy number and clinicopathological parameters was analyzed.
Results: 183 (93.8%) of 195 FISH-equivocal cases were of luminal subtype, while the other 12 (6.2%) were undetermined. Using 2018 ASCO/CAP guideline, all FISH-equivocal cases were recategorized to HER2 negative. Therefore, 31(15.9%) cases were luminal A-like, 152 (77.9%) were luminal B-like (HER2 negative) and 12 (6.2%) were triple negative. The average HER2 copy number showed positive correlation with chromosome 17 polysomy, but had no significant association with other clinicopathological parameters as well as prognosis. 17 (8.7%) cases were treated with trastuzumab, but showed no difference in prognosis with patients who didn’t receive targeted therapy.
Conclusions: In this study, all HER2 FISH-equivocal breast cancers were reclassified to be HER2 negative according to 2018 ASCO/CAP guideline. Most of these patients were luminal B-like (HER2 negative). The average HER2 copy number had no significant association with clinicopathological parameters, as well as prognosis.

Figure 1
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