Do Complex Mutations of the Epidermal Growth Factor Receptor Gene Reflect Intratumoral Heterogeneity?

Abstract

In our clinical practice, two different epidermal growth factor receptor (EGFR) gene mutations are occasionally found in a single tumor sample. Such co-occurring EGFR mutations have been termed “complex mutations,” and we have previously reported the incidence and efficacy of gefitinib for patients with complex mutations.1Hata A Yoshioka H Fujita S et al.Complex mutations in the epidermal growth factor receptor gene in non-small cell lung cancer.J Thorac Oncol. 2010; 5: 1524-1528Abstract Full Text Full Text PDF PubMed Scopus (60) Google Scholar In our previous article, we discussed the cause of complex mutations and speculated on the existence of intratumoral heterogeneity for EGFR mutations. We recently encountered three cases that support our hypothesis and herein present these cases. Case 1 was a 68-year-old man. He received a computed tomography-guided lung biopsy due to a suspicion of lung cancer. We performed a fine needle aspiration, followed by a core needle biopsy through a guide needle to obtain both cytological fluid and histological tissue (Figure 1). Although both cytology and histology revealed adenocarcinoma cells, we accidentally performed EGFR mutational analysis on both specimens. Interestingly, only a point mutation in exon 21 (L858R) was detected in the cytology, but complex mutations consisting of a point mutation in exon 18 (G719S) and L858R were detected in the histology. After a diagnosis of locally advanced disease, the patient underwent concurrent chemoradiation therapy. After the treatment, he has been observed and has not yet received EGFR-tyrosine kinase inhibitor (TKI) therapy. Case 2 was a 66-year-old woman. She was diagnosed with lung adenocarcinoma and underwent surgery as the initial therapy. EGFR mutational analysis in the surgical tissue revealed complex mutations consisting of a deletional mutation in exon 19 (Del-19) and L858R. After recurrence, she underwent multiple chemotherapies including EGFR-TKIs. In the course of treatment, she complained of gait disturbance and neck stiffness. Brain magnetic resonance imaging showed leptomeningeal metastases (Figure 2), and a lumbar puncture was performed. Unexpectedly, Del-19 disappeared, and only L858R was detected by EGFR mutational analysis of malignant cells in the cerebral spinal fluid. Rechallenge treatment with erlotinib was administered, and the clinical benefit has continued for 4 months. Case 3 was an 81-year-old man. He was initially diagnosed with lung adenocarcinoma with pleural disseminations. EGFR mutational analysis of the primary tumor showed complex mutations consisting of Del-19 and L858R. Considering the patient's age, gefitinib was chosen as the first-line treatment. Primary tumor and pleural disseminations markedly responded to gefitinib for approximately 20 months. However, the right pleural effusion has recently increased (Figure 3), and the cytology of pleural effusion revealed adenocarcinoma cells. Similarly, Del-19 disappeared, and both L858R and a point mutation in exon 20 (T790M) were detected by EGFR mutational analysis of the pleural effusion. Chest tube drainage has been carried out. Case 1 implies the existence of heterogeneous EGFR mutations in a single tumor: cytological fluid cells harboring only L858R and histological tissue cells harboring both G719S and L858R simultaneously existed in a single tumor. The intratumoral heterogeneity of EGFR mutation has been previously reported; both EGFR mutated and wild-type malignant cells were confirmed in a single tumor tissue in the report.2Sakurada A Lara-Guerra H Liu N et al.Tissue heterogeneity of EGFR mutation in lung adenocarcinoma.J Thorac Oncol. 2008; 3: 527-529Abstract Full Text Full Text PDF PubMed Scopus (50) Google Scholar In cases 2 and 3, although complex mutations consisting of Del-19 and L858R were detected at the initial EGFR mutational analysis, Del-19 has disappeared and L858R remained after EGFR-TKI treatments. Higher sensitivity to EGFR-TKIs in patients with Del-19 than L858R has been demonstrated in several reports.3Jackman DM Yeap BY Sequist LV et al.Exon 19 deletion mutations of epidermal growth factor receptor are associated with prolonged survival in non-small cell lung cancer patients treated with gefitinib or erlotinib.Clin Cancer Res. 2006; 12: 3908-3914Crossref PubMed Scopus (486) Google Scholar If Del-19 and L858R cells had existed separately, Del-19 cells would have responded to EGFR-TKIs better than L858R cells, and L858R cells might have remained. Our present cases exhibiting these complex mutations suggest the intratumoral heterogeneity of EGFR mutations. Considering intratumoral heterogeneity consisting of EGFR-sensitive-mutated cells and wild-type or EGFR-resistant-mutated cells, the detection of EGFR mutations using a highly sensitive polymerase chain reaction method from small biopsies may not always reflect whole tumor sensitivity to EGFR-TKIs.4Travis WD Rekhtman N Riley GJ et al.Pathologic diagnosis of advanced lung cancer based on small biopsies and cytology: a paradigm shift.J Thorac Oncol. 2010; 5: 411-414Abstract Full Text Full Text PDF PubMed Scopus (147) Google Scholar However, our data were taken from only a few cases, and further research is needed. The clinical significance of intratumoral heterogeneity warrants future studies.