The key facilitator of homologous recombination is Rad51 (see above) and Christodoulopoulos and colleagues found in 1999 that Rad51 (Figure 2C, yellow arrows) is activated by the alkylating agent chlorambucil (CLB) used in chemotherapy in B-CLL patients [107]. The gene discussed is RAD51; the disease is B-cell chronic lymphocytic leukemia.