EGFR mutations detected on cytology samples by a centralized laboratory reliably predict response to gefitinib in non–small cell lung carcinoma patients

BACKGROUND Epidermal growth factor receptor (EGFR) mutations are reliably detected by referral laboratories, even if most lung cancer cytology specimens sent to such laboratories contain very few cells. However, EGFR mutations may be distributed heterogeneously within tumors, thereby raising concerns that mutations detected on cytology are not representative of the entire tumor and, thus, are less reliable in predicting response to tyrosine kinase inhibitor (TKI) treatment than mutations detected on histology. To address this issue, the authors reviewed their clinical practice archives and compared the outcome of TKI treatment among patients who were selected by cytology versus patients who were selected by histology. METHODS From July 2010 to July 2012, 364 cytology samples and 318 histology samples were received. Exon 19 deletions and the L858R point mutation in exon 21, detected by fragment assay and TaqMan assay, respectively, were confirmed by direct sequencing; discrepancies were resolved by cloning polymerase chain reaction products. The response rate (RR) and progression‐free survival (PFS) at 12 months (range, 3‐34 months) were evaluable in 13 EGFR‐mutated patients who were selected for treatment by cytology and 13 patients who were selected by histology. RESULTS The mutation rate was similar in histology samples (8.5%) and cytology samples (8.8%). The RR (54%) and PFS (9.2 months) were similar in histologically selected patients and cytologically selected patients (RR, 62%; PFS, 8.6 months; P = .88). The disease control rate (responsive plus stable disease) was 92% in histologically selected patients and 100% in cytologically selected patients. CONCLUSIONS EGFR mutations detected on cytology specimens by a centralized laboratory can predict TKI treatment response equally well as mutations identified on histology samples. Cancer (Cancer Cytopathol) 2013;121:552–560. © 2013 American Cancer Society. The cytologic material sent to referral laboratories for the analysis of epidermal growth factor receptor mutations often contains only a few cells. This study demonstrates that the response to treatment with a tyrosine kinase inhibitor is predicted on routine cytology equally well as by mutations identified on histology samples.