Fine-needle aspiration cytology (FNAC) is a well-accepted procedure for the diagnosis and biological characterization of breast carcinoma. Estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2) status have a strong prognostic and predictive value in invasive breast carcinoma (IBC). ThinPrep (TP) cytology, which uses an alcohol-based fixative, is increasingly being used for immunocytochemistry. In this study, the authors compared the immunocytochemical evaluation of hormone receptors (HR) and HER2 on TP-processed FNAC with the immunohistochemical analysis performed on the corresponding formalin-fixed paraffin-embedded (FFPE) breast tumor specimens, which are considered the gold standard.
FNACs were performed on 116 primary IBCs at the time of diagnosis and subjected to immunocytochemical evaluation of HR and HER2 using the TP method. The same markers were immunohistochemical evaluated on the corresponding FFPE tissue specimens. HER2 fluorescent in situ hybridization analysis was performed only on the equivocal immunohistochemical results.
The HR results of the TP cytology specimens showed a very good agreement with those of the corresponding FFPE tissue samples (Cohen kappa test = 0.92; concordance rate = 98%) for estrogen receptor, and a good agreement (kappa = 0.76; concordance rate = 90.9%) for progesterone receptor. A perfect agreement (kappa = 1) was observed between TP and FFPE tissue samples in evaluating HER2 status.
Alcohol-based fixation seems not to affect the immunocytochemical evaluation of HR and HER2. Considering the high levels of agreement between the evaluation of HR and HER2, on both cytology specimens and on the corresponding FFPE tissue samples, the authors concluded that the TP technique can be routinely used for the biological characterization of IBC.