The stability of estrogen and progesterone receptor expression on breast carcinoma cells stored as preservCyt suspensions and as ThinPrep slides

BACKGROUND. Analysis of estrogen receptor (ER) and progesterone receptor (PR) status is an important ancillary test in the evaluation of positive breast fine-needle aspirates. This study compares the detection of ER and PR in breast carcinoma cells suspended in PreservCyt with that achieved with stored ThinPrep slides (TP). METHODS. ER and PR positive mammary tumor cells (cell line ZR-75-1 spiked in PreservCyt by the American Type Culture Collection) were used to evaluate the stability of immunodetection of ER and PR under two conditions: 1) TP slides prepared immediately from PreservCyt and stored air-dried (stored TP) for up to 56 days, and 2) TP prepared from cells suspended in PreservCyt (newly prepared TP) on Days 1, 2, 5, 14, 21, 42, and 56. At each of the time periods, stored TP and newly prepared TP were analyzed for ER and PR using the same immunocytochemical staining protocol. The percentage of positive cells was calculated by counting 1000 cells/TP. RESULTS. Positivity for ER and PR was demonstrated in both stored TP and newly prepared TP on Days 1, 2, 5, 14, 21, 42, and 56. Over the 56-day period, the number of ER positive cells ranged from 41% to 57% in stored TP and from 38% to 58% in newly prepared TP. The number of PR positive cells ranged from 31% to 41% in stored TP and from 26% to 37% in newly prepared TP. Mild, nonspecific cytoplasmic and nuclear staining occurred in all newly prepared TP (PR > ER). CONCLUSIONS. ER and PR antigenicity was preserved in both stored TP and newly prepared TP of mammary tumor cells over a 56-day storage period. This demonstrates that ER and PR status can be evaluated in cytologic material from breast carcinoma using the ThinPrep technique.