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Notch-1 Mutations Are Secondary Events in Some Patients with T-Cell Acute Lymphoblastic Leukemia

Authors' Affiliations: ¹ Department of Haematology, University College London; ² Department of Haematology, Royal Free Hospital; and ³ Great Ormond Street Hospital, London, United Kingdom

Requests for reprints: Marc R. Mansour, Department of Haematology, University College London, 98 Chenies Mews, London WC1E 6HX, United Kingdom. E-mail: m.mansour{at}ucl.ac.uk.

Purpose: Activating Notch-1 mutations are frequent in T-cell acute lymphoblastic leukemia (T-ALL), occurring in >50% of patients. In murine models of T-ALL, Notch-1 activation can both directly initiate leukemia and cooperate secondarily to other primary events. Whether acquisition of Notch-1 mutations is an early initiating event or a secondary event in the pathogenesis of human T-ALL is unclear.

Experimental Design: We used denaturing high-performance liquid chromatography, sequencing, and fragment analysis to analyze Notch-1 mutational status and mutant level in 62 patients at presentation as well as 16 matched presentation-relapse samples.

Results: We detected Notch-1 mutations in 47 patients (76%). Seven of these were low-level mutations (quantified at 10%), despite high blast counts, suggesting that they were acquired as a secondary event in a subclone. Of 16 matched presentation-relapse samples studied, 7 were wild-type at both presentation and relapse. Five of nine mutant-positive patients at presentation relapsed with the same mutation(s) at the same high level. Four patients had evidence of a change in mutant at relapse. One lost a PEST mutation and became wild-type. Two others lost mutations at relapse but acquired different mutations, despite unchanged T-cell receptor rearrangements, suggesting that the latter event predated the acquisition of the Notch-1 mutation. One relapsed with a secondary T-cell leukemia and different Notch mutation.

Conclusions: These results suggest that Notch-1 mutations can sometimes be acquired as secondary events in leukemogenesis and must be used cautiously as solitary minimal residual disease markers.

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