P35.07 Analysis of Inter-Tumor Heterogeneity Among Lesions in Autopsy Cases With Untreated Lung Cancer by DNA Methylation Profiling

Abstract

The clinical implications of intra-tumor heterogeneity in lung cancers have been widely investigated, with emphasis on the development of therapeutic resistance and disease recurrence. Because the collection of tumor tissue samples from various lesions in one patient is clinically impractical, very few investigations have evaluated the importance of inter-tumor heterogeneity (i.e., between the primary and metastatic lesions), which may play a significant role in determining the outcome of disease. Since DNA methylation, a major type of epigenetic modification, has been demonstrated to be involved in the development and/or progression of lung cancer, we assessed inter-tumor heterogeneity through the analysis of DNA methylation profiles in tissue samples collected at autopsy from patients with untreated lung cancer. DNA was extracted from the primary and metastatic lesions in pathologic autopsy samples obtained from 5 patients with untreated lung cancer (2 adenocarcinomas, 2 squamous cell carcinomas, and 1 small cell carcinoma). Since these patients were chemotherapy-naïve, the impact of anticancer therapy on the characteristics of the lesions was expected to be minimal. Using methylation-specific PCR, the aberrant DNA methylation profiles of 9 genes (p16, MDFI, CDH1, PCDH10, HOXD11, MLH1, RARB, TERC, and TIMP3) were assessed in all lesions. Patient #1, a 96-year-old woman with adenocarcinoma, exhibited heterogeneity of DNA methylation profiles between the primary and 10 metastatic lesions in 4 of 9 genes. Patient #2, an 85-year-old man with adenocarcinoma, exhibited differences between primary and 6 metastatic lesions in 5 of 9 genes. Patient #3, an 82-year-old man with squamous cell carcinoma, exhibited differences between primary and 11 metastatic lesions in 2 of 9 genes. Patient #4, a 77-year-old woman with squamous cell carcinoma, exhibited differences between primary and 12 metastatic lesions in 3 of 9 genes. Patient #5, an 86-year-old man with small cell carcinoma, exhibited differences between primary and 6 metastatic lesions in 6 of 9 genes.Tabled 1DNA methylation profiles of 9 genes in the primary and metastatic lesions of patient #1p16MDFICDH1TERCPCDH10HOXD11MLH1RARBTIMP3primaryRt. upper lobe of lung+++-++-+-metastasis #1Rt. parietal pleura+++-+--+-metastasis #2Lt. lobe of liver (1)-++-++-+-metastasis #3Lt. lobe of liver (2)-++-++-+-metastasis #4Rt. lobe of liver (1)-+--+----metastasis #5Rt. lobe of liver (2)-+--++---metastasis #6Lt. lower lobe of lung+++-+----metastasis #7Lt. upper lobe of lung-++-+--+-metastasis #8Lt. visceral pleura of lung-+--++---metastasis #9Rt. upper lobe of lung-++-++---metastasis #10Rt. lower lobe of lung-++-++-+- Open table in a new tab This study demonstrates that inter-tumor heterogeneity develops even in chemotherapy-naïve patients and suggests that epigenetic regulation may be one of the potential mechanisms underlying inter-tumor heterogeneity in lung cancers. In addition, the results of this study suggest that determining the origin of lesions (i.e., distinguishing the metastases from a primary lesion or other metastatic lesions) or distinguishing between a second primary and metastatic lung tumors by simply comparing the genomic characteristics between lesions may not be practical.