P. m., aged 4 years, has returned to the family doctor because of a recurrent sore throat and cough. her mother mentions unusual listlessness and anorexia. the physician notices several bruises on her legs and arms and one on her back. the doctor orders blood tests and a course of antibacterial drugs. test results indicate a low hemoglobin level, thrombocytopenia, and a high lymphocyte count, with abnormally high numbers of blast cells. following a bone marrow aspiration, a diagnosis of all is confirmed. describe the pathophysiology of acute lymphoblastic leukemia.