Inflammatory cells produce a proliferation inducing ligand (APRIL), one of the most recently cloned members of the tumor necrosis factor (TNF) family. Early experiments implicated APRIL as a promoting factor in the natural course of various cancers, reinforcing the concept that host inflammatory reactions are part of a tumor development. Recent studies have further analyzed the tumor-promoting role of APRIL in patients with solid tumors or with hematological malignancies. Here, we will review the recent literature, and provide evidence that APRIL may be a useful prognostic tool and a potential target in the treatment of some cancers.