Two possible reasons might have contributed to the difference in the samples that did not show concordance: (1) Even with ARMS technology, the poor quality DNA extracted from samples or low rate EGFR mutation which was beyond the sensitivity limit of the detection might have resulted in false negative; and (2), The tumor was genetically heterogeneous, which means that mutation-positive cells and mutation-negative cells co-existed,[16], [21] and/or in a mixed adenocarcinoma lung nodule,[22] different EGFR mutations could be demonstrated in various parts of the tumor. The gene discussed is EGFR; the disease is adenocarcinoma.