Histopathologic characteristics of pulmonary adenocarcinomas with and without EGFR mutation

EGFR mutation played crucial role for responsiveness of non-small cell lung cancers to EGFR tyrosine kinase inhibitors. Almost the mutations were present in adenocarcinomas. Few had studied on histopathologic correlation with EGFR mutation in pulmonary adenocarcinomas. To obtain better view on pathobiology of pulmonary adenocarcinomas, we correlated exons 19 and 21 mutations with various histopathologic features by dissecting particular histological patterns from 60 surgically resected adenocarcinomas.

Gland-forming pattern, including bronchiloloalveolar carcinoma (BAC), well-formed acinar, and poorly-formed acinar patterns more frequently contains EGFR mutations than solid pattern (72.7% vs. 23.1%, p = 0.002). EGFR mutations of each within the gland-forming pattern are not significantly different. Micropapillary pattern revealed less exon 19 mutations than the gland-forming pattern (12.5% vs. 66.7%, p = 0.018), but tended to have more Exon 21 mutations than the others (33.3% vs. 11.9%, p = 0.10). Tumors predominated by BAC pattern more commonly had exon 19 mutations than non-BAC predominated tumors (68.8% vs. 39.5%, p = 0.046). EGFR-mutated tumors comprised less proportion of papillary pattern than tumors without mutation (mean = 1.5% vs. 11.2%, p = 0.049). Terminal respiratory unit (TRU) histology was associated with more EGFR mutations (72.4% vs. 42.1%, p = 0.036). Tumors smaller than 3.5 cm had more EGFR mutations than larger tumors (73.1% vs. 41.9%, p = 0.018).

High frequency of the mutation does not present only in BAC pattern, but also in well-formed and poorly-formed acinar patterns, suggesting them as usual spectrum of EGFR mutated adenocarcinomas. Other characteristics of EGFR-mutated adenocarcinomas include TRU-type histology, smaller size, and less solid phenotype.