Metadata supporting data files of the related manuscript: Quantitative assessments and clinical outcomes in HER2 equivocal 2018 ASCO/CAP ISH group 4 breast cancer

The study quantified human epidermal growth factor receptor 2 (HER2) RNA and protein expression in 2018 American Society of Clinical Oncology/ College of American Pathologists (ASCO/CAP) in-situ hybridisation (ISH) group 4 (HER2/CEP17 ratio <2.0; average HER2 copy number ≥ 4.0 and <6.0; 2013 ASCO/CAP ISH equivocal) breast cancers. ISH Group 4 in the 2018 ASCO/CAP guidelines breast cancer is defined by ISH HER2/CEP17 ratio of <2.0 and HER2 copy number between 4.0 and 6.0. Little information about prognosis and response to anti-HER2 treatment is currently available for this subset of patients.

Data access:

The data files that support the figures, tables and the supplementary figures and tables in this article are not publicly available in order to protect patient privacy. The data files are available on reasonable request from the corresponding author Veerle Bossuyt, MD; Pathology Associates; Address: 55 Fruit Street, Warren, 202, Boston, MA 02114-2696; Email: vbossuyt@partners.org.

Patient consent: This study was approved by IRB protocol ID 9505008219, Yale University. Patients were selected by searching the Yale Pathology electronic database for samples of invasive breast carcinoma with HER2 ISH HER2/CEP17 ratio <2.0; average HER2 copy number ≥ 4.0 and <6.0 results from 2014 to 2017.

Data files:

The data file supporting figure 1 in the published article is in Excel file format and holds the results of analysis of HER2 immunohistochemistry (IHC) status by real-time quantitative reverse transcription polymerase chain reaction (RT-qPCR) and quantitative immunofluorescence (QIF).

The data file supporting figure 2 in the published article is in Excel file format and holds fluorescence in-situ hybridisation (FISH) HER2/ CEP17 ratios, FISH HER2 copy numbers and HER2 scores obtained by RT-qPCR and QIF in 63 patients.

The data file supporting figure 4 in the published article is in Excel file format and holds survival data according to trastuzumab treatment and HER2 status.

The data file supporting table 1 in the published article is in Excel file format and holds the clinicopathological characteristics of the 63 breast cancer patients.

The data file supporting table 2 in the published article is in Excel file format and holds outcome data for HER2 negative and HER2 2018 ASCO/CAP ISH group 4 and IHC2+ (IG4,2+) status patient cohort.

The data file supporting supplementary table 1 in the published article is in Excel file format and holds results of sensitivity and specificity assessments of HER2 RT-qPCR and QIF.

The data file supporting supplementary table 2 in the published article is in Excel file format and holds assessment of RT-qPCR and QIF results using trastuzumab outcome data.

The data file supporting supplementary table 3 in the published article is in Excel file format and holds outcome data from estrogen receptor (ER)-positive and ER-negative patients.

Study aims and methodology:

Breast cancers in 2018 ASCO/CAP ISH group 4 between 2014 and 2017 were identified from the Yale archives. 63 patients (34 with HER2 immunohistochemistry (IHC) status 0/1+ and 29 with HER2 IHC status 2+) were included in the study. Patient characteristics, systemic treatments, and outcomes were compared. The authors assessed HER2 by real-time quantitative reverse transcription polymerase chain reaction (RT-qPCR) and quantitative immunofluorescence (QIF) to evaluate HER2 mRNA and protein levels respectively.

The study aimed to determine whether ISH group 4 breast cancers represent a distinct biological group and whether with additional information following trastuzumab treatment, this might help to guide treatment decisions in these patients.