ABSTRACT
Epidermal growth factor receptor (EGFR) gene mutation examination is now performed in most medical institutions in order to select the molecular targeted medicine for lung cancer. It became clear that the positive rate of the biopsy material was lower than that of the surgical sample in this hospital. The cause was attributed to false negatives due to low tumor cell content in biopsy specimens. We investigated the presence of the mutation using surgical samples and preoperative biopsy specimens from the same patients in 13 cases. Furthermore, we investigated the tumor cell content of the biopsy specimens by cell counting. Results showed that 3 of 6 biopsy specimens that were associated with positive surgical samples were judged to be negative. The tumor cell content was less than 5% in all negative cases. Regarding EGFR gene mutation examination, we should carefully determine tumor cell content when using biopsy specimens.