"High-ICR": A Unifying Data-Driven Reporting System for Her2 FISH Analysis Based on Intra-Tumor Heterogeneity.
Rodney A Schmidt, Suzanne M Dintzis, Kim H Allison. University of Washington, Seattle
Background: The College of American Pathologists Expert Panel (CAP-EP) proposal for reporting intra-tumoral heterogeneity for Her2 by FISH is based on the number of individually amplified cells and a presumed definition of individual cell amplification. We explored a large set of breast cancer cases to determine objectively the degree of individual cell amplification that is most likely appropriate and assessed a novel reporting system based on that definition.
Design: We collected data from 1329 consecutive breast cancer cases analyzed for Her2 amplification by FISH using the Abbott PathVysion Her-2 DNA probe kit, including Her2 and CEP17 counts from 32,116 individual cells. Both individual cell ratios (ICR) and overall case ratios were calculated. The lowest ICR characteristic of amplified cases was determined by comparing the ICRs found in cases classified as amplified by both CAP-EP and CAP/ASCO ratios (Consensus Amplified (CA); n=136) with those of cases considered non-amplified by both criteria (Consensus Non-amplified (CNA); n=763) and with those of the remaining cases (n=430).
Results: CA, CNA and other cases are all composed of multiple ICR populations. There is essentially no overlap between the ICRs of CA and CNA cases; cells of the remaining cases span both groups but are predominantly those of CNA cases. An ICR of 4.0 is the lowest that identifies amplified cases. Using ICR>=4 to define "High-ICR" cells, cases are divided into Amplified (>90% High-ICR cells), Non-amplified (<=10% High-ICR cells) and Heterogeneous (>10 to 90% High-ICR cells). High-ICR classification correlates closely with CAP/ASCO ratio reporting (below) but differs markedly from CAP-EP criteria due to different treatment of cells with ICRs of 2.5 and 3.