[18,23,28,29,30] In our previous study, we have demonstrated that immune cells, endothelial cells, and to a lesser extent cancer cells are sources of ADA1 iso-enzyme activity in breast cancer, while circulating monocytes and most probably tumor-associated macrophages are a dominant source of intra- and extracellular ADA2 activity. The gene discussed is ADA; the disease is breast carcinoma.