Immunostaining of estrogen receptor, progesterone receptor, MIB1 antigen, and c-erbB-2 oncoprotein in cytologic specimens: a simplified method with formalin fixation.

An effective but simple fixation protocol for the immunocytochemical staining of cytologic smears for estrogen and progesterone receptors, the Ki-67 antigen (using MIB1 antibody), and c-erbB-2 protein is described. One hundred twenty-seven smears from a variety of malignant and benign breast lesions showed good preservation of antigenicity when subjected to the following fixation protocol: Freshly made smears were air-dried for 20 min to 14 h at 22 degrees C before immersing in 10% buffered formalin for 2-14 h. Immunostaining followed microwave-stimulated epitope retrieval. There was strong concordance of staining with corresponding tissue sections in 15 cases of malignant tumors (ER: r = 0.7381; PR: r = 0.6684; MIB1: r = 0.7234). Immunostaining staining, when delayed for 5-10 days in about half the smears, showed no noticeable difference in reactivity, attesting to effective storage of the formalin-fixed smears at room temperature.