Treatment with CD40 ligand decreased proliferation of BT-20 and T-47D cells which are CD40-positive, but did not change the growth of CD40-negative breast cancer cell lines, as detected in MCF-7 or ZR-75-1 cells (Esteva et al., 2007), supporting the idea that CD40–CD40LG axis modulates proliferation of cancer cells. The gene discussed is CD40LG; the disease is breast carcinoma.