Mutational inactivation of the ATM gene has been demonstrated in mantle cell lymphoma, T-cell prolymphocytic leukemias, rhabdomyosarcomas, and gastric cancer [28]–[31], and ATM heterozygous state is more common in breast cancer patients than in the general population [32], [33]. The gene discussed is ATM; the disease is T-cell prolymphocytic leukemia.