Diagnosis Discrepancy from Different Original Specimen in PCR EGFRMutation Test

Epidermal growth factor receptor (EGFR) mutation status guides treatment in non-small cell lung cancer; del E746-A750 in exon 19 and p.L858R in exon 21 are the most common mutations. We present a patient whose initial lymph node and computed tomography-guided pathology led to a suspicion of poorly differentiated carcinoma; however, during the clinical course, no obvious tumor origin was noted, and the pathologic morphology favored the squamous type. Not until the EGFR mutation status of secondary sites was checked did we confirm the disease origin as the lung.