Genomic Profiles Associated with Early Micrometastasis in Lung Cancer: Relevance of 4q Deletion

PURPOSE: Bone marrow (BM) is a common homing organ for early disseminated tumor cells (DTC) and their presence can predict the subsequent occurrence of overt metastasis and survival in lung cancer. It is still unclear whether the shedding of DTC from the primary tumor is a random process or a selective release driven by a specific genomic pattern. EXPERIMENTAL DESIGN: DTCs were identified in BM from lung cancer patients by an immunocytochemical cytokeratin assay. Genomic aberrations and expression profiles of the respective primary tumors were assessed by microarrays and FISH analyses. The most significant results were validated on an independent set of primary lung tumors and brain metastases. RESULTS: Combination of DNA copy number profiles (array CGH) with gene expression profiles identified five chromosomal regions differentiating BM-negative from BM-positive patients (4q12-q32, 10p12-p11, 10q21-q22, 17q21 and 20q11-q13). Copy number changes of 4q12-q32 were the most prominent finding, containing the highest number of differentially expressed genes irrespective of chromosomal size (p=0.018). FISH analyses on further primary lung tumor samples confirmed the association between loss of 4q and the BM-positive status. In BM-positive patients 4q was frequently lost (37% vs. 7%), whereas gains could be commonly found among BM-negative patients (7% vs. 17%). The same loss was also found to be common in brain metastases from both small and non-small-cell lung cancer patients (39%). CONCLUSIONS: Thus, our data indicates for the first time that early hematogeneous dissemination of tumor cells might be driven by a specific pattern of genomic changes. In the present study, we investigated whether the early dissemination of tumor cells into BM is associated with a specific molecular pattern in primary lung cancer. For the detection of DTCs, we used an immunocytochemical cytokeratin (CK) assay that allows the identification of one tumor cell in the background of one million normal BM cells . The specificity of this assay was previously demonstrated by the analysis of almost 200 non-carcinoma control patients . By using high-resolution comparative genomic hybridization (CGH) and expression arrays we compared the genomic aberration and expression profiles of lung carcinomas from patients with and without DTCs in the BM. A three step analysis with independent measurement technologies revealed tumor-specific genetic signatures associated with early hematogeneous dissemination of NSCLC cells into BM. Interestingly, the most prominent aberration identified was also frequently observed in brain metastases, suggesting a potential involvement in both tumor cell dissemination and metastatic progression.