Examination of a peripheral blood smear demonstrates a leukemia composed of small mature lymphocytes without blast forms. Which of the following is the most likely age of this patient?

Different leukemias tend to affect populations of different ages. The disease described is chronic lymphocytic leukemia (CLL), which is a disease of older adults. Both the one year-old and the five year-old would be most likely to have acute lymphocytic leukemia (ALL). The 45 year-old would be likely to have either AML or chronic myelogenous leukemia (CML).