Immunocytochemical evaluation of estrogen receptor on archival Papanicolaou-stained fine-needle aspirate smears.

The availability of limited fine-needle aspirate smears necessitates the selection of immunocytochemical (IC) methods that allow reuse of Pap-stained smears to assess the estrogen receptor (ER) status of breast carcinoma. The objective of the current study was to compare IC evaluation of ER status on FNA smears by three methods: 1) ER-ICA using H222 monoclonal antibody performed on slides fixed in formaldehyde-methanol-acetone; 2) destained Pap slides using 1D5 antibody; and 3) Pap-stained slides without destaining using the same 1D5 antibody. Two representative Pap smears of breast carcinoma were selected from 48 cases of breast carcinoma in which ER was previously evaluated by ER-ICA. One of these Pap smears was used as such and the other was destained prior to immunostaining by a modified ABC method using 1D5 monoclonal antibody. The number of cells with positive nuclear staining was expressed as a percentage and the intensity of staining was semiquantitatively scored on a scale of 1+ to 3+. The degree of agreement between the three methods was evaluated statistically by weighted kappa statistics. Thirty cases (63%) showed varying degrees of positive staining while 18 cases (38%) were entirely negative by all three methods. Significant discrepancies in the number of cells with positive staining and in the intensity of staining between the three methods occurred in 40% and 23% of the cases and was mainly due to a reduction in the number of cells with positive staining and the intensity of staining using Pap slides in comparison to ER-ICA. Weighted kappa agreement of the percentage of cells with positive staining using Pap-stained slides and destained Pap-slides in comparison to ER-ICA was 0.75 and 0.64, respectively, and that for the intensity of staining was 0.75 and 0.66, respectively. Therefore, IC evaluation of ER using Pap-stained smears as such or destained Pap smears compared favorably with ER-ICA. However, Pap-stained smears used as such for ER immunostaining showed a slightly better agreement with ER-ICA than destained Pap smears. Because significant differences in ER-IC staining can occur with any of the immunocytochemical methods, a negative result is less reliable as an indicator of true ER status than a positive result.