Using a transplantable fibrosarcoma cell line transfected with cDNAs of the active forms of IL-1β, i.e., the mature form of IL-1β or the mature form of IL-1β ligated to a signal sequence (ssIL-1β), in which IL-1β is actively secreted through the endoplasmic reticulum-Golgi pathway, we observed that invasiveness of the different tumor cell lines was directly proportional to the amount of IL-1β secreted by the malignant cells (Song et al., 2003, 2005). Here, IL1B is linked to fibrosarcoma.