Immunohistochemistry results can be further evaluated by a semiquantitative approach used to assign an H-score (or “histo” score) to tumor samples.^1,2 First, membrane staining intensity (0, 1+, 2+, or 3+) is determined for each cell in a fixed field. The H-score may simply be based on a predominant staining intensity, or more complexly, can include the sum of individual H-scores for each intensity level seen. By one method, the percentage of cells at each staining intensity level is calculated, and finally, an H-score is assigned using the following formula:

[1 × (% cells 1+) + 2 × (% cells 2+) + 3 × (% cells 3+)]

The final score, ranging from 0 to 300, gives more relative weight to higher-intensity membrane staining in a given tumor sample. The sample can then be considered positive or negative on the basis of a specific discriminatory threshold. ■

References

1. Hirsch FR, Varella-Garcia M, Bunn PA Jr, et al: Epidermal growth factor receptor in non-small-cell lung carcinomas: Correlation between gene copy number and protein expression and impact on prognosis. J Clin Oncol 21:3798-3807, 2003.

2. John T, Liu G, Tsao M-S: Overview of molecular testing in non-small-cell lung cancer: Mutational analysis, gene copy number, protein expression and other biomarkers of EGFR for the prediction of response to tyrosine kinase inhibitors. Oncogene 28:S14-S23, 2009.