Context.—
Evaluation of HER2 gene amplification by fluorescence in situ hybridization (FISH) was changed by recent American Society of Clinical Oncology/College of American Pathologists (ASCO-CAP) guidelines.
Objective.—
To determine frequencies and assess patterns of HER2 protein expression for each ASCO-CAP guideline FISH category among 7526 breast cancers accrued to our consultation practice.
Design.—
We retrospectively reevaluated the HER2 FISH status of breast cancers in our consultation practice according to ASCO-CAP FISH guidelines, and documented HER2 protein levels in each category.
Results.—
—According to new guidelines, 17.7% of our consultation breast cancers were “ISH-positive” with HER2:CEP17 FISH ratios ≥2.0 and average HER2 gene copies per cell ≥4.0 (group 1); 0.4% were “ISH-positive” with ratios ≥2.0 and average copies <4.0 (group 2); 0.6% were “ISH-positive” with ratios <2.0 and average copies ≥6.0 (group 3); 4.6% were “ISH-equivocal” with ratios <2.0 and average copies ≥4.0 and <6.0 (group 4); and 76.7% were “ISH-negative” with ratios <2.0 and average copies <4.0 (group 5). However, only groups 1 (HER2 amplified) and 5 (HER2 not amplified) agreed with our previously reported status, and only these groups demonstrated the expected immunohistochemistry status, overexpression and low expression, respectively. Groups 2 and 4 breast cancers lacked overexpression, whereas group 3 was not significantly associated with either increased or decreased HER2 expression.
Conclusions.—
Although the status of approximately 95% of our cases (groups 1 and 5) is not affected by the new guidelines, those of the other 5% (groups 2–4) conflict with previous HER2 gene amplification status and with HER2 status by immunohistochemistry.
Impact of an alternative chromosome 17 probe and the 2013 American Society of Clinical Oncology and College of American Pathologists guidelines on fluorescence in situ hybridization for the determination of HER2
gene amplification in breast cancer