The minimum number of neoplastic cells currently recommended to evaluate HER2 gene amplification in breast cancer is not sufficient

Recently it was published in Histopathology a work developed by the Department of Pathology of the Ipatimup Diagnostics in collaboration with Hospital Pedro Hispano and Hospital Prof. Doctor Fernando Fonseca concerning the minimum number of neoplastic cells needed to quantify robustly the amplification of the HER2 gene in breast cancer.
The work consisted in evaluating the amplification status of the HER2 gene in breast carcinoma by 4 different observers using increasing numbers of neoplastic cells. The authors concluded that the minimum number of neoplastic cells currently recommended in international guidelines (20 cells) is not sufficient and should be increased to at least 40 cells. In addition, cases with doubtful amplification should be subjected to a second evaluation by an experienced observer.

Authors and Affiliations:

António Polónia ^1,2, Catarina Eloy ^1,2, João Pinto ³, Ana Costa Braga ^4,5, Guilherme Oliveira ¹, Fernando C. Schmitt ^1,2,6
1 Department of Pathology, Ipatimup Diagnostics, Ipatimup, University of Porto, Porto, Portugal
² FMUP, Faculty of Medicine, University of Porto, Porto, Portugal
³ Department of Pathology, Hospital Pedro Hispano, ULS Matosinhos, Matosinhos, Portugal
⁴ Department of Pathology, Hospital Prof. Doutor Fernando Fonseca, EPE, Amadora, Portugal
⁵ NOVA MEDICAL SCHOOL - Faculdade de Ciências Médicas, Universidade Nova de Lisboa, Lisboa, Portugal
⁶ Laboratoire National de Santé, Dudelange,Luxembourg

Abstract:

AIM: To evaluate the intraobserver and interobserver reproducibility of the HER2 in-situ hybridization (ISH) test in breast cancer by measuring the impact of counting different numbers of invasive cancer cells.
METHODS AND RESULTS: A cohort of 101 primary invasive breast cancer cases were evaluated for HER2 gene amplification by silver ISH, and the concordance among four observers with different levels of experience, counting different numbers of invasive cancer cells, was determined. The evaluation of the samples included scoring 20 nuclei, in three different areas. The cases were scored twice, with a washout interval of at least 2 weeks. We observed an increase in the intraobserver concordance rate between the first and second evaluations with an increase in cell count. A count of 60 invasive cells was needed to obtain a concordance rate near 95% and an agreement rate greater than 0.80 by all observers. The interobserver concordance rate of the HER2 test also increased with the increase in cell count, reaching at least a 90% concordance rate with a count of 60 invasive cells. The median variability of both the HER2/CEP17 ratio and the average HER2 copy number between different evaluations decreased with the increase in cell count, being statistically higher in HER2-positive cases.
CONCLUSIONS: The minimal cell number recommended in current guidelines should be raised to at least 40, and preferably 60, invasive cells. Moreover, cases with amplification levels close to the threshold should be subjected to a dual count from an experienced observer.

Journal: Histopathology

Link: http://onlinelibrary.wiley.com/doi/10.1111/his.13208/abstract