Morphological changes in previously frozen formalin-fixed paraffin-embedded (FFPE) tissue.

Frozen sections are the mainstay of intraoperative consultation in the daily practice of surgical pathology. In the vast majority of cases, they are employed to guide the surgeon’s hand by determining whether a tumour is benign or malignant, determining the histological type and tumour grade, the extent of tumour involvement, or the status of surgical margins.1 2 In most pathology practices, the residual frozen tissue is formalin-fixed and paraffin-embedded (FFPE) and submitted as the frozen section control block. This is done for quality assurance purposes by monitoring the accuracy of the frozen section diagnosis.3 Prior freezing alters the preservation of morphological features in the subsequent FFPE tissue. It can also have an impact on the preservation of antigens and immunoreactivity for commonly used immunohistochemical stains. One study found that immunostaining for S-100 protein, HMB-45, synaptophysin and neuron specific enolase was lost in previously frozen tissue but positive in unfrozen tissue, while chromogranin and carcinoembryonic antigen showed significantly decreased staining.4 Prior freezing of glioma tissue has been reported to lead to false-negative staining results for IDH1.5 It is for …