Increased risk of neurological relapse in acute lymphoblastic leukemias with high levels of cerebrospinal fluid thymidine kinase at diagnosis.

Cerebrospinal fluid thymidine kinase (CSF-TK) was measured at diagnosis in 62 patients with acute lymphoblastic leukemia (ALL) without initial neurological manifestations, who achieved a complete remission after chemotherapy. During the follow-up period, 10 patients developed central nervous system (CNS) involvement. At the onset of the disease mean CSF-TK levels in these subjects were found to be significantly higher than those observed in patients without subsequent CNS complications. In particular, 7/10 (70%) of these patients who presented CSF-TK levels above the upper limit of normal (1.4 U/microliters) had evidence of a neurological relapse, while 49/52 (94.2%) of subjects with presenting CSF-TK levels of up to 1.4 U/microliters did not develop a neurological leukemic disease (p < 0.00001). The white blood cell count at diagnosis was significantly increased, but not directly correlated to CSF-TK levels, in the group with CNS involvement, while age, serum thymidine kinase levels and lactic dehydrogenase, FAB classification or immunophenotype were not different in patients with or without neurological relapse. In conclusion, increased levels of CSF-TK at presentation correlate with a high risk of subsequent CNS involvement in patients with responsive ALL.