The Effect of 96-Hour Formalin Fixation on the Immunohistochemical Evaluation of Estrogen Receptor (ER), Progesterone Receptor (PR), and HER2 Expression in Invasive Breast Cancer
Isil Z Yildiz-Aktas, David J Dabbs, Mamatha Chivukula, Rohit Bhargava. University of Pittsburgh Medical Center, PA
Background: Accurate ER, PR and HER2 results are essential for proper therapeutic-decision making in breast cancer treatment. The ASCO/CAP guidelines recommend formalin fixation for up to 72 hours for ER/PR, and up to 48 hours for HER2. Our aim was to study the impact of 10% neutral-buffered formalin fixation of 96 hours on ER/PR and HER2 testing by immunohistochemistry by comparing core biopsies fixed under current ASCO/CAP guidelines to resection samples fixed for 96 hours.
Design: Tissues were collected prospectively and fixed in 10% neutral-buffered formalin for 96 hours. An attempt was made to include cases with weak to moderate receptor expression. Of the 47 cases, for ER, 6 were negative, 5 were weak, 9 were moderate, and 27 were strongly positive. For PR, 12 were negative, 11 were weak, 15 were moderate, and 9 cases were strongly positive. For HER2, 4 were scored 0, 12 were 1+, 24 were 2+, and 7 were 3+. All cases were run on the Benchmark XT, using antibody clones SP1 (ER), 1E2 (PR) and 4B5 (HER2). Scoring for ER/PR was performed using the semi-quantitative H-Score method, with an H-score of 1 considered positive. ASCO/CAP guideline scoring was used for HER2.
Results: Of the 47 cases, only one case (2%) showed a qualitative change in result. However, this change was a positive ER result (H-score of 1) on 96 hours resected sample compared to a negative ER result (H-score of 0) on core biopsy. ER H-scores remained the same on 19 cases (40%), was lower on 17 cases (36%) and higher on 11 cases (23%). PR H-score remained the same on 21 cases (45%), was lower on 15 cases (32%) and higher on 11 cases (23%). For HER2, the IHC score remained the same on 46 cases (98%) and changed from 0 to 1+ on one case (2%).
Conclusions: Our results indicate no clinically significant difference in qualitative assessment of ER, PR, and HER2 results due to formalin fixation for 96 hours. The results do show slight difference in quantitative H-scores for hormone receptors, but we favor tumor heterogeneity and/ or intra-observer variability as the cause for this slight variation rather than prolonged fixation, as the variation occurred in both directions. ER, PR and HER2 immunohistochemical results should be considered valid for cases fixed for up to 96 hours.
Monday, March 19, 2012 1:00 PM
Poster Session II # 68, Monday Afternoon