Michael F. Press, Ivonne Villalobos, Angela Santiago, Roberta Guzman, Monica Cervantes, Armen Gasparyan, Anaamika Campeau,Yanling Ma, Denice D. Tsao-Wei, and Susan Groshen (2016) Assessing the New American Society of Clinical Oncology/College of American Pathologists Guidelines for HER2 Testing by Fluorescence In Situ Hybridization: Experience of an Academic Consultation Practice. Archives of Pathology & Laboratory Medicine In-Press.

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Assessing the New American Society of Clinical Oncology/College of American Pathologists Guidelines for HER2 Testing by Fluorescence In Situ Hybridization: Experience of an Academic Consultation Practice

Michael F. Press , MD, PhD; Ivonne Villalobos , MHA; Angela Santiago , BS; Roberta Guzman ; Monica Cervantes , BA; Armen Gasparyan ; Anaamika Campeau , BA; Yanling Ma , MD; Denice D. Tsao-Wei , MS; Susan Groshen , PhD

From the Departments of Pathology (Drs Press and Ma; Mss Villalobos, Santiago, Guzman, Cervantes, and Campeau; and Mr Gasparyan) and Preventive Medicine (Ms Tsao-Wei and Dr Groshen), Norris Comprehensive Cancer Center, University of Southern California, Los Angeles.

Reprints: Michael F. Press, MD, PhD, Department of Pathology, USC/Norris Comprehensive Cancer Center, 1441 Eastlake Ave, NOR5409, Los Angeles, CA 90033 (email: press@usc.edu).

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.