11115 Background: Tumor-stroma interaction plays a significant role for malignant growth. Results from prostate and breast cancer rodent models show cancerogenic properties of tumor-associated and genetically altered stromal cells (SC) when combined with initiated or normal epithelium (Olumi et al., Cancer Res 1999, Kuperwasser et al., PNAS 2004). However, data on the mechanisms and sequels of tumor-stroma interaction in lung cancer are scanty. Methods: Here, we analyzed the functional and molecular sequels of cross-talk between the non-small cell lung cancer (NSCLC) cell lines A549, H23, and H1703 and primary stromal cells (SC) derived from matched normal lung tissue and tumors of newly diagnosed NSCLC patients. Tumor cells were kept in a non-contact co-culture system with SC and analyzed for alterations in proliferation, colony formation, migration, adhesion, invasion, chemosensitivity and gene expression by Affymetrix HG U133 Plus 2.0 arrays. Results: Exposure to SC altered cellular functions and gene expression profiles related to tumor growth, metastasis and response to therapy. Each cell line showed individual alterations that were hierarchically governed by the (1) type of tumor cell, (2) the SC donor and his histology (3) and the local origin of the SC (normal lung tissue vs. tumor-associated). Conclusions: This in vitro model demonstrates an individual pattern of tumor-stroma interaction in NSCLC that is determined by both, the properties of the tumor cells and those of the stromal environment. Thus, biomarker programs in NSCLC should also consider the stromal compartment. No significant financial relationships to disclose.