A Consortium for Analytic Standardization in Immunohistochemistry

Consortium for Analytic Standardization in Immunohistochemistry

Overview

• Authors: Steven A. Bogen, MD, PhD; David J. Dabbs, MD; Keith D. Miller, FIBMS; Søren Nielsen, BLS; Suzanne C. Parry, BSc(Hons), MSc, FIBMS; Matthias J. Szabolcs, MD, PhD; Nils t'Hart, MD, PhD; Clive R. Taylor, MD, PhD; Emina E. Torlakovic, MD, PhD.

• Funding: Supported by a grant from the National Cancer Institute.

• Purpose: Aiming to improve accuracy and reproducibility of immunohistochemistry (IHC) tests through integration of analytic standards into routine practice.

Importance of Analytic Standards

• Key Stakeholders: Commercial vendors, biopharmaceutical firms, pathologists, scientists, clinical laboratories, external quality assurance organizations, and regulatory bodies.

• Role in Testing: Essential for assay development, validation, and method transfer into routine clinical assays. Recognized as critical quality assurance tools.

Objectives of the Consortium

• Mandates:

  1. Determine analytic sensitivity thresholds for selected IHC assays.

  2. Educate stakeholders on the nature and importance of analytic standards and their applications.

• Outcome: Publish data and provide recommendations for analytic sensitivity.

Need for CASI

• Lack of Standards: Unusual absence of analytic standards in the clinical diagnostic testing environment for IHC, critical for patient care.

• Technical Challenges: Previous efforts to develop standards faced difficulties, leading to inconsistencies in assay performance.

• Illustrative Example: Differences between two laboratories in estrogen receptor (ER) testing—one assay was significantly more sensitive than the other.

Data Analysis and Comparison

Case Study of ER Testing

• Laboratory A: Lower limit of detection (LOD) at 7310 molecules per cell.

• Laboratory B: LOD of 74,790 molecules per cell; significant disparity in sensitivity leads to inconsistent test results.

• Issue: Without analytic standards, it's unclear which laboratory's test is more accurate or clinically useful.

Implications of Lack of Standards

• Lack of link to clinical trial assays, causing uncertainty in optimal sensitivity for patient response predictions.

• Historical Example: ER expression responsiveness is not always associated with higher analytic sensitivity in practice.

Introducing IHC Calibration

Development of Calibrators

• Testing in Studies: Calibrators introduced for quantitative measurement in IHC analyses, linking to NIST standards.

• Measurement Process: IHC staining of calibrators performed similarly to tissue samples, allowing visualization of staining intensity correlated with analyte concentration.

• Analytic Response Curve: Illustrative of how calibrators can establish LOD and improve assay performance.

Analytical Standards Definition

• Definition and Types:

  • Primary Reference Standards: Core materials with known analyte concentrations prepared by recognized labs.

  • Secondary Reference Standards: Calibrators used in clinical laboratories, traceable to primary standards.

• Current State: Standards exist for other fields of laboratory medicine but not yet systematically for IHC.

Addressing IHC Testing Challenges

IHC Testing Deficiencies

• High rates of inadequate testing and discrepancies due to absence of analytic standards, potentially ranging from 10% to 30%.

• Patient Benefits:

  1. Increased accuracy and precision of tests.

  2. Development of new IHC assays.

  3. Foundation for more objective test result reporting.

Purpose of IHC Calibration

• Link Between Trials and Practice: Standards help maintain consistency between initial assays and later laboratory tests.

• Detection Cutoff Importance: Establishing a well-defined cutoff enhances diagnostic reliability.

Assay Management

Analytic Drift Control

• Concept: Analytic drift affects all assays; calibrators can mitigate the impact on test results.

• Example Scenarios: Simulation depicting how drift can alter test results between assays lacking consistent benchmarks.

Clarifications on Image Analysis

• Image analysis tools are ineffective without underlying analytic standards, potentially compounding inaccuracies in results.

CASI's Strategy and Structure

Study Execution

• Methodology: Engage clinical laboratories to participate in studies linking clinical sensitivity with analytic sensitivity by using tissue microarrays and calibrators.

• First Projects: Focus on HER2, PD-L1, p53, and BRAF V600E assays.

Organizational Framework

• Steering Committee: Composed of experts responsible for study design, data analysis, and recommendations.

• Management of Survey Data: Analysis of IHC tests helps gauge interlaboratory variability and identifies optimal analytic sensitivities.

Future Directions

• Extension of Standards: Emphasizing the importance of establishing analytic standards in IHC practices for future diagnostics.

• Collaboration Appeal: Encouraging stakeholders to engage with CASI for the development of improved diagnostic standards.

References

• Detailed citations from various studies underpinning the discussion of IHC analytic standards and the operationalization by CASI.