Expression profiling reveals a set of seven genes that may be required for lymph node metastasis in lung and breast cancer

Proc Amer Assoc Cancer Res, Volume 47, 2006 4296 Studies suggest that although cancer cells can potentially invade the blood vessels to gain access to the general circulation, the lymphatics are typically used for the initial spread of solid tumors. To identify membrane-bound or secreted proteins required for metastasis in lymphatic tissue, we first performed two separate microarray analyses using Affymetrix U133A chips whereby expression values of a pool of normal lymph node tissue (n=4) were compared to either 1) four non-small cell lung cancer (NSCLC) cell lines, or 2), three metastatic lymph nodes derived from breast cancer patients. Separate lists of the 35 most highly overexpressed genes were generated for each cancer type. Each list contained 20 tissue-specific genes and 15 potential cancer-specific genes. Seven genes were common to both lists (p< 3.5E-18; chi-squared test), of which two (EpCAM1, EpCAM2) encoded membrane-bound cell adhesion proteins, while one (XAG) encoded a secreted protein known to be involved in breast cancer metastasis. Real-time RT-PCR analysis of formalin-fixed paraffin embedded mediastinal lymph nodes (MLN) obtained from NSCLC patients confirmed that EpCAM1, EpCAM2, and XAG were highly overexpressed in metastatic MLN compared to control negative lymph nodes (AUC values = 0.97-1.00; 95% CI = 0.87-1.00). We provide evidence that Ese-1/Elf3, a potential transcriptional regulator of EpCAM1 identified from an in silico search using the CGAP NCI60 cancer cell line database, was also highly overexpressed in metastatic MLN, along with other potential Elf3-regulated genes Mal2 and Spint2. Preliminary data indicate that EpCAM1&2, S100P, XAG, Elf3, as well as sonic hedgehog, are also overexpressed in metastatic pancreatic cancer lymph nodes. Our results provide evidence that lymph node metastases in several cancers may require a set of at least seven genes, some of which appear to be transcriptionally regulated by Elf3.