ABSTRACT
In patients with epidermal growth factor receptor (EGFR) mutation-positive lung cancer (LC) who have acquired resistance to first and/or second-generation EGFR-tyrosine kinase inhibitors (EGFR-TKIs), detection of EGFR T790M (T790M) mutation is essential before administration of osimertinib. Tissue sample is the main specimen used to detect the T790M mutation, and so cell block preparation using pleural or pericardial fluid should be considered. The utility of body cavity effusion cell block methods in T790M mutation detection have not yet been fully evaluated. This study aimed to evaluate the clinical background and treatment course of LC patients harboring the T790M mutation by using body cavity effusion cell block methods at our hospital. All patients were treated with first and/or second-generation EGFR-TKIs and had developed malignant pleural or pericardial fluid as a result of progressive disease. T790M mutation status was evaluated using body cavity effusion cell block method in 9 patients, from April 2016 to August 2017. We retrospectively evaluated the clinical characteristics and treatment course of these 9 patients (3 males and 6 females; median age 76 years). At the first diagnosis of LC, 7 patients had stage IV cancer; 4 patients were diagnosed by bronchial fibroscopy and 3 were diagnosed from pleural fluid examination. Regarding EGFR mutation, 3 and 6 patients carried the exon 19 deletion and L858R mutation, respectively. Median time interval between the first diagnosis of LC and T790M mutation evaluation was 30.8 months; 7 patients were diagnosed with positive T790M mutation by using body cavity effusion cell block methods. The T790M mutation was highly detected by examination of body cavity effusion cell blocks. Further evaluation is necessary with respect to variations in T790M detection rate based on the specimen collection site and/or progressive disease pattern in different patients.