Successful lung cancer EGFR sequencing from DNA extracted from TTF-1 immunohistochemistry slides: a new means to extend insufficient tissue.

Lung cancer biopsy material is limited and is used for morphologic diagnosis and immunohistochemical and molecular testing. This can lead to tissue exhaustion, resulting in repeat biopsies (when clinically possible), delayed testing, and increased risks. Consequently, there is a need to optimize preanalytical specimen use for molecular testing. Although hematoxylin/eosin can be used for as a DNA source for molecular testing, little is known regarding the potential use of immunohistochemistry (IHC) slides, as these are subject to harsh conditions that can lead to DNA degradation. Our aim was to evaluate whether DNA extracted from TTF-1 IHC slides, a common stain for lung adenocarcinoma, can be tested for EGFR mutations. Twenty-two lung adenocarcinoma samples (11 EGFR wild type and 11 mutated) were selected. Slides were stained for TTF-1 IHC. Following TTF-1 staining, tissue underwent DNA extraction. Pyrosequencing for mutations in exons 18, 19, 20, and 21 of EGFR was performed, and results were compared to clinical EGFR testing data. All 22 TTF-1 samples produced successful results, and 21 were concordant. Of the 11 originally EGFR-mutated cases, 10 TTF-1 samples showed identical mutations in all exons of interest. One case with an L858R mutation on original testing was negative on sequencing of the TTF-1 sample, possibly due to lower tumor burden on the TTF-1 stained slide. All 11 originally EGFR wild-type cases showed identical results on the TTF-1 samples. TTF-1 IHC slides can be a viable DNA source for molecular testing, especially important in lung biopsies with insufficient material following diagnostic evaluation.