The role of tumor-associated macrophages and other innate immune cells in metastatic progression of lung cancer

There is increasing evidence that the immune cells within the tumor microenvironment play a key role in the ability of tumor cells to proliferate and spread. Given that macrophages are the most frequent hematopoietic cells found in the tumor microenvironment, they play an especially important part in tumor biology. There are numerous mechanisms by which tumor-associated innate immune cells can influence most aspects of the metastatic process. They play a role in the epithelial to mesenchymal transformation occurring in the original tumor cells and enhance basement membrane breakdown by the cancer cells invading neighboring tissue, lymph nodes, and blood vessels. Tumor-associated innate immune cells have been shown to have a crucial role in angiogenesis, in immunosuppression, and eventually in priming distant sites for the development of metastases. Unfortunately, we still know relatively little about the roles of these cells in lung cancer. Further work in animal models and using patient lung cancer samples is very much needed. With this knowledge, a better understanding of the role that these cells play in the metastatic process may facilitate development of new therapeutics, as well as the recognition of new diagnostic and prognostic markers. Modulation of the metastatic phenotype through intervention in the host innate immune response remains a promising future area of cancer therapy.