Abstract 44: Monitoring of metastasis by detection of EGFR mutation, T790M, with plasma using animal model for metastasis of human lung cancer

Monitoring of metastasis by detection of EGFR mutation, T790M, with plasma using animal model for metastasis of human lung cancer Epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKI) significantly prolonged survival of lung cancer patients carrying EGFR activating/sensitive mutations. However, most patients eventually acquire resistance to EGFR-TKI, and the half of mechanisms of acquired resistance has been reported to be the secondary EGFR mutation, T790M. To monitor the existence of T790M, we have developed a novel detection system, named mutation-biased PCR and quenched probe system (MBP-QP) method. Since the system is highly sensitive, T790M could be detected using circulating plasma DNA (ctDNA). Recurrence of lung cancers frequently occurs as lymphogenic and/or hematogenous metastases. Metastasis has been thought to be caused by evolution of cancer cells which happens during treatment. In primary lesion, intra-tumor heterogeneity has been evidenced from the view point of molecular events as well as morphological aspects, and the cancer cells which acquired metastatic potency spread to whole body. Based on these mechanisms, molecular characteristics between primary and metastatic lesions are different, and sensitivity to anti-cancer agents also differs between them. In addition, metastasis consists of several steps such as loss of cell adhesion, intravasation, survival in circulation, exit into new tissues, and colonization in a distant site. Therefore, a suitable animal model is indispensable for investigation of metastasis. We have established the animal model showing metastases into the whole body using the xenograft of human lung cancer cells in immunodeficient mouse, NOD/SCID/JAK3null (NOJ), which were produced by crossing NOD-scid and JAK3null mice. The xenograft model injected by human lung cancer cell line, H1975, using NOJ mice showed lymphogenous and hematogenous metastases. The difficulty for analysis of metastasis in animal model is monitoring of metastasis. Recently, in vivo imaging systems using luciferase-labeled cancer cells have been applicable to animal experiments, but the expensive device and luciferase transfected cells should be prepared. In this model, we introduce the monitoring system of metastasis using ctDNA isolating form peripheral blood. Since H1975 is human lung cancer cell line carrying T790M and L858R, these mutations could be detected in ctDNA using MBP-QP system. The detection rate of T790M and/or L8