Testing the Limits: Reevaluation of the Upper Limit of Formalin Fixation Time Recommended in the ASCO/CAP HER2 Testing Guidelines.
Samantha Redfield, Diana Bell, Luminita Rezeanu, Alexandra Shaye Brown. The University of Mississippi Medical Center, Jackson
Background: The guideline recommendations for HER2 testing published by the College of American Pathologists (CAP) state that breast tumors submitted for HER2 testing should be fixed in 10% neutral phosphate buffered formalin (NBF) for no more than 48 hours prior to processing. One of the concerns for this upper limit cut-off time is the fact the excess cross-linking of proteins caused by prolonged formalin fixation can lead to false negative immunohistochemistry (IHC) results. This cut-off presents significant performance issues for laboratories that do not routinely embed tissues on weekends, since specimens received on Fridays will not be embedded until Monday mornings. The purpose of this study is to evaluate this recommended upper limit of formalin fixation time to determine if it could be adjusted from 48 hours to 72 hours, as is currently recommended by CAP for estrogen / progesterone assays.
Design: In this study, all invasive breast carcinoma specimens received in our laboratory on Fridays were processed routinely, with our histotechnologists embedding tissue early on Monday mornings. Both immunohistochemistry (IHC) and fluorescence in situ hybridization (FISH) were performed on all specimens using FDA-approved assays (HercepTest, Dako; PathVysion kit, Abbott). The results from the 23 cases that were negative for HER2 by IHC were compared to results of HER2 FISH, as defined by the CAP guideline recommendations.
Results: The IHC results of the 23 cases of invasive breast carcinoma that were HER2 negative (either 0 or 1+, as defined by the CAP HER2 guideline reccomendations) after fixation in 10% NBF for greater than 48 hours, but less than 72 hours showed a 100% correlation with the HER2 FISH results.
Conclusions: The CAP recommendation for the upper limit of formalin fixation for HER2 testing could potentially be increased from 48 hours to 72 hours. We did not find any disagreement between IHC and FISH results for specimens that were fixed in 10% NBF for greater than 48 hours but less than 72 hours. By adjusting the suggested upper limit of formalin fixation, the recommendations for fixation time would be the same for both HER2 and estrogen / progesterone assays, which would make standardization of fixation times more efficient. For laboratories that do not employ histotechnologists to embed tissue on weekends, changing the upper limit of fixaton time is more cost-effective than hiring additional staff of paying existing staff overtime. It also decreases costs to the patient since IHC is less expensive than FISH.
Tuesday, March 1, 2011 9:30 AM
Poster Session III # 46, Tuesday Morning