Usefulness of tissue microarrays for assessment of protein expression, gene copy number and mutational status of EGFR in lung adenocarcinoma.

Specific inhibitors targeting the epidermal growth factor receptor (EGFR) can increase survival rates in certain lung adenocarcinoma patients with mutations in the EGFR gene. Although such EGFR-targeted therapies have been approved for use, there is no general consensus among surgical pathologists on how the EGFR status should be tested in lung adenocarcinoma tissues and whether the results of immunohistochemistry (IHC), fluorescence in situ hybridization (FISH), and mutational analysis by molecular methods correlate. We evaluated the EGFR status in 61 lung adenocarcinomas by IHC (using total and mutant-specific antibodies against EGFR), by FISH analysis on tissue microarrays (TMAs), and by direct sequencing. The results of each method were compared using χ² and κappa statistics. The sensitivity and negative predictive value estimating the presence of abnormal EGFR for each test was calculated. The results show that, with respect to expression patterns and clinicopathological parameters, the total and mutant-specific EGFR detected by immunohistochemistry and FISH analysis on TMAs are valid and are equivalent to conventional methods performed on whole-tissue sections. Abnormal EGFR was detected in 52.4% of patients by IHC, FISH, and sequencing. The best sensitivity (100%) and negative predictive value (100%) was determined by evaluating the EGFR status with all methods. Testing for molecular changes in EGFR using a single test is likely to underestimate the presence of EGFR abnormalities. Taken together, these results demonstrate the high potential of TMAs to test for the major mechanisms of EGFR activation in patients with lung adenocarcinoma.

Assessment of morphology, antigenicity, and nucleic acid integrity for diagnostic thyroid pathology using formalin substitute fixatives.

BACKGROUND: With the advent of the formaldehyde standard law in France, and because of the impact of new methods for diagnosis and prognosis in pathology, formalin replacement in surgical pathology laboratories is currently being discussed in France. However, a set of criteria must be assessed before introducing a formalin substitute fixative. The objective of this study was to compare formalin substitute fixation with formalin fixation and cryoconservation of tissues from several benign and malignant thyroid pathologies with respect to morphology, antigenicity, and nucleic acid (RNA, DNA, microRNA) integrity. METHODS: Calibrated specimens (200 mg, 1 cm(2) each) from four conventional papillary thyroid carcinomas, four follicular variant of papillary thyroid carcinomas, three minimally invasive follicular carcinomas, four thyroid adenomas, five thyroid nodular hyperplasias, and five normal thyroid tissues were fixed for 6, 12, or 24 hours, in different fixatives (formalin, Glyo-Fixx, FineFIX, ExcellPlus, RCL2) at room temperature or at 4 degrees C. Tissues were stained (hematoxylin-eosin, periodic acid Schiff, trichromic Masson, and Sweet-Gordon staining) and their antigenicity determined by immunohistochemistry (performed with HBME-1, galectin-3, CK19, vimentin, CD31, and KL1 antibodies). Evaluation by four pathologists was made blinded. The quantity and quality of DNA, RNA, and two representative microRNA extracted from deparaffinized sections of paraffin embedded specimen were compared with that of cryosections. RESULTS: The staining and morphology were not altered by the use of different fixatives. However, formalin, FineFIX, and RCL2 gave the best results for immunohistochemistry. Moreover, FineFIX and RCL2 gave the highest amount of nucleic acids and of the best quality. CONCLUSIONS: All the formalin substitute fixatives used in this study provided good histomorphologic quality for the different stained thyroid tissues, but individually, some fixatives performed better for immunohistochemical and molecular biological procedures for different thyroid pathologies.