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Genetic heterogeneity (GH) is a rare but important event in the evaluation of HER2 amplification status. We investigated whether HER2 fluorescence in situ hybridization (FISH) GH correlated with increased protein expression by immunohistochemistry (IHC) and/or morphologic features using image analyses. Retrospective search of HER2 FISH GH cases 2016-2020 was performed. Cases with both FISH and IHC slides available were considered eligible and were digitally imaged. Additional demographic, histological, and treatment information was compiled from pathology and medical records when available. Overall, 11 of 15 cases (73.3%) had HER2 FISH GH that matched to areas of HER2 overexpression or focally different morphology. Nine cases with areas of gene amplification overlapped with10% of intense circumferential protein expression ("Mini 3+"), and 1 case with focal micropapillary features. Clinical information was available on 6 patients (40%), all were alive with no evidence of disease (mean follow-up 30.5 months; range, 12-65 months). One patient with GH and a lymph node metastasis showed nonamplified population in the nodal tumor. GH, when defined as discrete clusters of amplified cells following 2013 ASCO/CAP guidelines, even when less than 10% of the tumor cells, frequently has morphologic correlates such as focal intense protein overexpression or micropapillary morphology. Clinical significance of these focal gene amplification and protein overexpression needs to be further investigated. |
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