RAI1 alternate probe identifies additional gastroesophageal adenocarcinoma cases as amplified following equivocal HER2 fluorescence in situ hybridization testing: experience from a national reference laboratory

Abstract Objectives To review impact of the ASCO/CAP 2018 update on HER2 testing. Methods HER2 fluorescence in situ hybridization (FISH) test requests from primary and metastatic breast cancers between August 2018 and January 2019 were included. FISH results requiring a changed algorithm under the new guidelines (groups 2, 3, and 4) were identified and HER2:CEN17 ratios, average HER2, CEN17 signals/cell, and HER2 immunohistochemistry (IHC) results were recorded. Results Of the HER2 FISH cases 176/812(21.7%) fell within groups 2, 3, or 4; 0/12, 1/12, and 2/152 cases were positive (3+) by IHC, and 1/12, 2/12, and 6/152 cases were positive after targeted scoring from groups 2, 3, and 4, respectively. Following 2018 updates, 8.3%, 25%, and 5.3% of the groups 2, 3, and 4 were positive, respectively. Conclusions Groups 2, 3, and 4 constituted over 20% of HER2 FISH tests in a reference laboratory. The 2018 ASCO/CAP update significantly decreased the HER2 positivity rate.

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Working Up Group 4 Equivocal HER2 Samples Tested by Fluorescence in Situ Hybridization in a Reference Laboratory Setting: Past, Present, and Future

Journal of Clinical Oncology ◽

10.1200/jco.19.02482 ◽

2020 ◽

Vol 38 (2) ◽

pp. 175-176

Author(s):

Katherine B. Geiersbach ◽

Reid G. Meyer ◽

Daniel R. Sill ◽

Taofic Mounajjed ◽

Beiyun Chen ◽

...

Keyword(s):

In Situ Hybridization ◽

Fluorescence In Situ Hybridization ◽

Reference Laboratory ◽

Laboratory Setting ◽

Group 4

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RAI1 Alternate Probe Identifies Additional Breast Cancer Cases as Amplified Following Equivocal HER2 Fluorescence In Situ Hybridization Testing: Experience From a National Reference Laboratory

Archives of Pathology & Laboratory Medicine ◽

10.5858/arpa.2016-0201-oa ◽

2016 ◽

Vol 141 (2) ◽

pp. 274-278 ◽

Cited By ~ 10

Author(s):

Ling Hui ◽

Katherine B. Geiersbach ◽

Erinn Downs-Kelly ◽

H. Evin Gulbahce

Keyword(s):

In Situ Hybridization ◽

Fluorescence In Situ Hybridization ◽

False Negative ◽

Metastatic Breast ◽

Her2 Status ◽

Reference Laboratory ◽

Breast Cancers ◽

Negative Results ◽

Control Probe

Context.—In 2013 the American Society of Clinical Oncology and College of American Pathologists updated the HER2 guidelines and changed the equivocal category for HER2 in situ hybridization testing to an average HER2 copy number of 4.0 to 5.9 with a HER2:CEP17 ratio of less than 2.0 and proposed retesting, with an option of using another control probe to avoid false-negative results. RAI1, located at band position 17p11.2, is a popular alternate probe locus for retesting equivocal changes. Objective.—To review experience with the RAI1 alternate probe in HER2 fluorescence in situ hybridization equivocal breast cancers. Design.—Primary and metastatic breast cancers with equivocal HER2 fluorescence in situ hybridization, retested with an alternate (RAI1) probe, were identified. HER2, RAI1, and CEP17 copy numbers, HER2 to control probe ratios, and genetic heterogeneity were recorded. Hematoxylin-eosin–stained slides were reviewed for type and grade of cancer. Results.—Of 876 cases tested with CEP17 as the reference probe, 97 (11.1%) had equivocal HER2 fluorescence in situ hybridization results. Additional testing with the RAI1 probe classified 39.2% cases (38 of 97) as amplified with a HER2:RAI1 ratio ranging from 2.0 to 3.2 (mean, 2.37); 3.1% (3 of 97) were still unclassifiable because of a deletion of RAI1. Conclusions.—RAI1 identified close to 40% of original HER2 fluorescence in situ hybridization equivocal cases as amplified, making these patients eligible for targeted therapies. It is not known whether guidelines for US Food and Drug Administration–approved probes can be extrapolated to alternate probes when an alternate control probe shows losses or gains. Because of the lack of guidelines for reporting HER2 status with alternate probes, laboratories face challenges in interpreting results.

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