Estimation of hormone receptor status in fine‐needle aspirates and paraffin‐embedded sections from breast cancer using the novel rabbit monoclonal antibodies SP1 and SP2

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Abstract
We describe a method of immunocytochemical assessment of estrogen receptor (ER) status on alcohol‐fixed smears obtained by fine‐needle aspiration (FNA) from breast cancer patients, using a commercially available rabbit monoclonal antibody anti‐ER (SP1) without any antigen retrieval. A series of 40 aspirates were analyzed and the results of ER status were compared with the respective formalin‐fixed tissue using the same procedure and with assessment by the classical method using the mouse monoclonal antibody 6F11 (anti‐ER) with antigen retrieval on paraffin sections. Twenty‐four out of the 40 cases examined were positive at least by two methods and 16 were negative for all three determinations. The results obtained in the ER immunocytochemical assay on aspirates and paraffin sections using the antibody SP1 and those obtained on paraffin sections using the antibody 6F11 were quite similar. In one case the material was insufficient to interpret the reaction in the cytological specimen and only one case, with focal positivity reaction on paraffin sections, was negative in the cytological specimen. The intensity of nuclei staining in cytological smears of breast cancer cells was stronger than that observed by traditional methods. We also assessed progesterone receptor (PR) status on 40 paraffin‐sections from breast cancer patients, using a commercially available rabbit monoclonal antibody anti‐PR (SP2), with the same characteristics described for anti‐ER (SP1). The results were compared with assessment by the classic method with mouse monoclonal antibody 1A6 (PR) on paraffin sections and total agreement was observed. Of the 40 cases examined, 18 were positive and 22 were negative for the two determinations. We conclude that the application of the ER method on alcohol‐fixed smears / paraffin sections with the rabbit monoclonal antibody SP1, and the PR method on paraffin sections with the rabbit monoclonal antibody SP2, provide several advantages, such as high sensitivity and specificity of the reaction, stronger immunostaining, shorter procedures times, and avoidance of antigenic retrieval methods. Diagn. Cytopathol. 2003;29:207–211.