Title

Abstract 5444: Real-time RT-PCR of terminal deoxynucleotidyl transferase (TdT) is a useful tool for identification of minimal leukemia in cerebrospinal fluid

Document Type

Presentation

Department

Biological and Biomedical Sciences; Haematology/Oncology

Abstract

Accurate detection of central nervous system (CNS) involvement in children with newly diagnosed acute lymphoblastic leukemia (ALL) could have profound prognostic and therapeutic implications. The detection of cerebrospinal fluid (CSF) infiltration by leukemic cells as performed by morphological assessment is subjective and unable to detect low levels of involvement. Therefore, newer and more accurate techniques are required to more efficiently detect minimal leukemic cell involvement. For this reason, a quantitative, Real-time RT-PCR targeting the TdT molecule was developed and tested to allow an objective and sensitive methodology for detecting CNS leukemia. 35 diagnostic CSF samples were subjected to the qRT-PCR assay for TdT. Only 4/35 samples were positive by cytomorphological detection. Of these 4 samples, one sample was diagnosed with CNS disease (CNS 3) and three samples had lower numbers of leukemic blasts (CNS 2). When compared to morphology results, as the gold standard, we found 24 out of the 35 samples to be positive by qRT-PCR. 20 CSF samples that were negative by morphology had detectable TdT by RT-PCR, possibly indicating leukemic infiltration below the level of cytomorphological detection. Serial samples for the 4 CNS-positive patients were tested by qRT-PCR and showed persistent positivity with gradual reduction in quantity of TdT with chemotherapy administration. 11 samples had no detectable TdT by RT-PCR and were found to be negative by cytomorphological assessment as well. In patients with no cytomorphologically detected blasts, TdT positivity was not associated with the level of peripheral blood WBC count. This methodology provides an objective, quantitative and sensitive tool for the detection of leukemic blasts in the CSF. This allows us to detect molecular CNS involvement in CNS negative patients. Although the outcome for all CNS negative patients is good, this has been achieved with fairly intensive prophylactic CNS-directed therapy, reduction in CNS-directed therapy may be possible in molecularly negative patients.

Comments

This work was published before the author joined Aga Khan University

Publication

Cancer Research

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