The relationships between PDCD4, miRNA-21, inflammation and tumorigenesis therefore need to be reconciled, which includes how miRNA-21 and possibly other microRNAs secreted in exosomes by activated macrophages in the tumour microenvironment during inflammation can downregulate the expression of epithelial PDCD4 and promote tumorigenesis. The gene discussed is PDCD4; the disease is neoplasm.