Immunohistochemical detection of estrogen and progesterone receptor and HER2 expression in breast carcinomas: comparison of cell block and tissue block preparations.

Fine needle aspiration (FNA) is a rapid tool for detection of breast carcinomas. Evaluation of estrogen and progesterone receptors (ER, PR) and HER2 expression by immunohistochemistry (IHC) are routinely performed in breast carcinomas. Formalin fixation of tissue for a minimum of 6 hours, and for HER2 not more than 48 hours is the current recommended practice. In this retrospective study, we compared ER, PR and HER2 expression in breast carcinomas using archival ethanol-fixed FNA cell block with formalin fixed resection tissue block preparations. 34 archival breast carcinoma FNA cell blocks of primary origin with subsequent resection tissue blocks were identified retrospectively. All 34 cases were diagnosed as invasive ductal carcinoma. Cases with neoadjuvant or adjuvant chemotherapy were excluded. Cell blocks were initially fixed in 50% ethanol (4-12 hrs), followed by formalin fixation (minimum 6 hrs). Tissue blocks were formalin-fixed within 4-8 hrs for 6-48 hrs. ER, PR, and HER2 IHC results on the cell blocks and tissue blocks were compared. Alcohol fixed cell block samples for detection of ER and PR by IHC show good agreement with tissue block samples and are therefore a reliable method (weighted Kappa of 0.773 and 0.785, respectively) to triage patients for hormonal treatment. However, HER2 results show only moderate agreement with a weighted kappa of 0.571. The increase in discrepant results may be due to ethanol fixation which results in false positive increased HER2 expression. These results demonstrate the importance of adherence to the College of American Pathologists/ASCO guidelines for HER2 IHC.