Previously, our group demonstrated that 8-Cl-Ado (Figure 1A) is tumoricidal to primary CLL lymphocytes [12], breast cancer [2], myeloma [17], and mantle cell lymphoma (MCL) [8] cell lines and this cytotoxicity was dependent on the analog’s metabolism to its monophosphate form by adenosine kinase [9] followed by triphosphate accumulation. The gene discussed is ADK; the disease is breast carcinoma.