The importance of IL-16 in regulation of cell cycle and growth is underscored by the findings that the cells of certain cancers lack the IL-16 gene or have mutations in nuclear localization sequence of the protein, preventing its entrance to the nucleus and resulting in hyperproliferative states (86, 87), as was demonstrated in cutaneous T cell lymphoma (CTCL) (88). The gene discussed is IL16; the disease is primary cutaneous T-cell non-Hodgkin lymphoma.