Acute Myeloid Leukemia with Mutated NPM1 Presenting with Life-Threatening, Either Arterial or Venous, Thromboembolism: a Report of 4 Cases.

Abstract 4135

Acute myeloid leukemia (AML) expressing mutated NPM1 gene and cytoplasmic nucleophosmin (NPMc+ AML) [Falini B et al, NEJM 2005;352:254-266] is a new entity of WHO classification that shows distinctive biological and clinical features. AML with mutated NPM1 usually presents with a high white blood cell count; the bone marrow biopsy is usually markedly hypercellular and leukemic cells frequently show myelomonocytic or monocytic features, with dysplasia and involvement of two or more cell lineages in about 25% of cases. Lack, or low expression, of CD34 in over 90% of cases is the most distinctive immunophenotypic feature of NPM1-mutated AML and is independent of leukemic cell maturation. NPM1 gene mutation without concomitant FLT3-ITD identify a subgroup of AML patients with a favorable prognosis and has been associated with an approximately 50-60% probability of survival at 5 years in younger patients. Here we report 4 out of 41 (10%) patients, admitted at our Hospital in the last year, with new-diagnosed AML with mutated NPM1 presenting with life-threatening thromboembolic (either arterial or venous) events. The main characteristics of these patients are summarized in Table 1. The patients had neither personal nor family history concerning thromboembolism. Hyperleukocytosis was a common feature of the vast majority of NPM1-mutated AML patients at diagnosis. Immunophenotypic analysis did not show a peculiar phenotype in these patients.

In two patients (cases 1 and 2), the arterial thromboembolic event (acute myocardial infarction and acute ischemia of right lower limb, respectively) presented about one month before diagnosis of leukemia. In the other 2 patients (cases 3 and 4), deep venous thromboembolism was concomitant with the diagnosis of leukemia. One patient (case 4), who could not initiate chemotherapy for severe concomitant renal failure, died few days after diagnosis. The other patients recovered from the acute event and upon diagnosis of leukemia were promptly treated with standard polychemotherapy which allowed to obtain complete hematological remission associated with complete resolution of the thromboembolic event. The clinical course after chemotherapeutic treatment of the patients outlines the importance and life saving role of early chemotherapy even under adverse circumstances. The pathogenesis of thromboembolic disease in hematological malignancies is complex and multifactorial: tumor cell-derived procoagulant, fibrinolytic or proteolytic factors and inflammatory cytokines affect clotting activation. Other important factors include infectious complications and hyperleukocytosis. However, large vessel thrombosis is a very rare clinical presentation. Our report of severe thromboembolic events at presentation in AML with mutated NPM1 suggests some still unidentified biological features of this leukemia which we are currently investigating.