Evaluation of the HER2 and Hormone Receptor Status in Metastatic Breast Cancer Using Cell Blocks: A Multi-Institutional Study.

OBJECTIVE: We explore the problems associated with the cell block (CB) method for receptor analysis in breast cancer metastases and propose a method for reporting the results.

STUDY DESIGN: Nine institutions used the CB method for the analysis of hormone receptors (HRs) and HER2 (human epidermal growth factor receptor 2) protein in cytological specimens of breast cancer metastases in routine practice. The stained slides were independently evaluated by 8 pathologists. Dual in situ hybridization assay was performed in cases of discordant results for HER2 protein. Based on the results, we propose a method for receptor scoring in the CB method.

RESULTS: Of 61 specimens, 57 contained tumor cells. Two or more pathologists disagreed on the results for the estrogen receptor, progesterone receptor, and HER2 protein in 3 (5.3%), 13 (22.8%), and 19 (33.3%) cases, respectively. The discrepant results for the HRs were attributed to the presence of a few positive cells or faintly stained cells. The high interobserver discordance rate for HER2 protein was explained by interobserver differences in the scoring criteria.

CONCLUSION: The use of categorical scoring into positive and negative is recommended for evaluating the HR expressions. Use of strict criteria for HER2 protein 2+ and 3+ cases is recommended, as HER2-positive cases should not be missed.