Molecular Pathology Laboratory Network

ASCO/ CAP guidelines prescribe a standardized ischemic time of < one hour and a rigid window of formalin fixation time ranging from 6 to 48 hours in 10% neutral buffered formalin (NBF) but not any other fixatives for HER2 breast cancer testing.

Guidelines appear to have improved immunohistochemistry/ FISH correlations and decreased expensive repeat HER2 testing, which is unquestionably a positive result. However, in many laboratories they have created logistical and cost issues. As a natural result, some investigators seek objective support for less restrictive limits to the preanalytic limits prescribed by ASCO/CAP.

Authors used a single, very large tumor sample to compare processing per ASCO/ CAP guidelines with prolonged fresh, 4 day ischemic storage at 4°C, simulating a long weekend of prolonged cold-storage followed by fixation in 10% NBF, Pen-Fix, Bouin solution, Sakura Tissue-Tek Xpress, zinc formalin, or 15% NBF for time intervals ranging from 0 hrs to 7 days. HER2 immunohistochemical staining results were accurate beyond ASCO/ CAP guidelines for cold-ischemic time, fixation time and fixative-type, and Bouin solution was unacceptable for HER2 FISH testing. HER2 FISH results remained accurate for prolonged cold-ischemic times and prolonged NBF fixation times but were not consistently accurate with non-neutral buffered formalin fixatives which produced significant, variable rates of hybridization failure.

By my reading, this paper does not support the use of non NBFs for breast cancer HER2 testing. Even though HER2 immunohistochemistry was accurate with non NBFs, one never knows when reflex FISH testing will be required or requested.

Neda A. Moatamed et al. (2011). Effect of Ischemic Time, Fixation Time, and Fixative Type on HER2/neu Immunohistochemical and Fluorescence In Situ Hybridization Results in Breast Cancer: Am J Clin Pathol 136:754-761

Editorial. Guy E.Nichols MD, PhD.

MPLN offers HER2 testing in addition to a range of other molecular and immunohistochemistry tests for breast cancer. For more information about these tests contact a client service specialist at 800.932.2943.