The objective of this study is to determine the efficacy and safety of imatinib mesylate in patients diagnosed as having Philadelphia chromosome positive acute lymphocytic leukemia (ALL).

Inclusion Criteria:

• Patients with histologically confirmed diagnosis of ALL.
• Patients confirmed to be Ph chromosome positive or bcr-abl gene positive.
• Patients in relapse
• Patients refractory to initial remission induction therapy
• Patients ineligible for initial remission induction therapy
• Patients with an ECOG Performance Status Score from 0 to 2
• Serum creatinine concentration of not more than 2 × the upper limit of the normal range (ULN)
• AST (SGOT) and ALT (SGPT) of not more than 3 × ULN. In patients with hepatic dysfunction from leukemic involvement, AST (SGOT) and ALT (SGPT) should be not more than 5 × ULN
• Serum bilirubin level not more than 3 × ULN

Exclusion Criteria:

• Patients with findings indicative of leukemic involvement of the central nervous system
• Patients with any serious concomitant medical condition (e.g., poorly controllable infection, interstitial pneumonia, pulmonary fibrosis, congestive cardiac failure, poorly controlled diabetes mellitus, mental disorder)
• Patients expected to receive any hematopoietic stem cell transplantation within 6 weeks of the planned initiation of the study drug
• Patients having received any hematopoietic stem cell transplantation who have a Grade 3 or 4 GVHD.

Other protocol-defined inclusion/exclusion criteria may apply.