¹Servei de Laboratori, Hospital de Mataró, Mataró, Barcelona, Spain

²Laboatori de Citologia Hematològica, Laboratori de Referència de Catalunya, Hospital del Mar, IMAS, Barcelona, Spain

Correspondence to: J-A Hernández Rivas, Servei de Laboratori, Hospital de Mataró, Carreta de Cirera s/n, 08303, Mataró, Barcelona, Spain; Fax: 34-937417706

TO THE EDITOR

Progression of essential thrombocythemia (ET) to myelodysplastic syndromes (MDS) or acute myeloid leukemia (AML) is a rare event in patients who have not received antineoplastic agents.¹ However, therapy with alkylating agents, radiophosphorous or hydroxyurea has a leukemogenic risk, about 4.5% at 8 years.² No typical morphology or cytogenetic features of secondary MDS and AML in patients diagnosed with ET have been described. However, some cases of 17p^- syndrome, characterized by pseudo Pelger-Hüet hypolobulation and small vacuoles in neutrophils, deletion 17p and p53 mutations, have been described in patients with AML and MDS following ET treated with hydroxyurea.^2,3 We report on a case of AML in an untreated ET patient with structural abnormalities on 17p different from the 17p^- syndrome. To our knowledge, this is the first case of AML with 17p rearrangement in a patient with ET previously untreated.

In 1989, a 72-year-old woman was admitted with persistent thrombocytosis (platelet count 632 ´ 10⁹/l) in the absence of symptoms. According to the criteria of the Polycythemia Vera Study Group a diagnosis of ET was made.⁴ No therapy was administered. Ten years later, the patient was evaluated again because of fatigue. Physical examination showed a moderately reduced performance status, pallor and no organomegaly. Hematologic laboratory findings included hemoglobin of 87 g/l, mean corpuscular volume 92 fl, reticulocytes 51 ´ 10⁹/l, white blood cell count 3.3 ´ 10⁹/l (30% blast cells) and platelet count 1351 ´ 10⁹/l. Bone marrow aspirate was hypercellular, showing trilineage myelodysplasia, mostly of the megakaryocytic line. No pseudo Pelger-Huët or small vacuoles in the neutrophils were present. An infiltration of 39% of myeloblastic cells were observed. Bone marrow trephine biopsy showed trilineage myelodysplasia with reticulin but no collagen fibrosis. No ringed sideroblasts were present. Leukemic cells displayed CD13, CD33, CD34, CD117, CD123 and HLA DR antigens. Conventional cytogenetic analysis showed the following karyotype: 46,XX,add(17)(p13)[14]/46,XX[6]. Cross-species color banding FISH (Rx-FISH; Applied Imaging, Sunderland, UK) was performed showing a duplication of a region from chromosome 17 at 17p13. No other numerical or structural abnormalities were observed. Double-colour FISH performed with a specific probe for the BCR/ABL fusion genes (Vysis, Stuttgart, Germany) did not show BCR/ABL fusion. In adition, FISH analysis of the p53 gene (Vysis) did not show loss of the p53 gene. A diagnosis of AML was established. Three months later, hydroxyurea was initiated because of very high thrombocytosis (3351 ´ 10⁹/l). The patient remains alive 13 months after diagnosis with supportive and hydroxyurea therapy.

Leukemic transformation of ET is infrequent. Most of them are related to patients who received cytoreductive treatment during the chronic phase.⁵ In contrast, few cases of acute leukemia after untreated ET have been reported and most of them without cytogenetic alterations.⁶ The present patient developed AML 10 years after the diagnosis of ET and she had never been treated. No specific morphological or immunophenotypic characteristics were present in the case reported here. In fact, she had untreated ET with an acute transformation to AML displaying no typical dysgranulopoiesis of 17p^- syndrome in the bone marrow. Interestingly, the patient showed a structural rearrangement of 17p (a duplication at 17p13, demonstrated by Rx-FISH) without involvement of the p53 gene. Nevertheless, conventional cytogenetics and Rx-FISH did not allow the precise identification of the duplicated region from chromosome 17. The case reported illustrates that the acute transformation of ET may also occur in the absence of chemotherapy, as it is well known in other myeloproliferative disorders.⁷ Morover, the structural rearrangement on 17p without involvement of the p53 gene did not show the morphological and clinical characteristics of patients with 17p^- syndrome.

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2 Sterkers Y, Preudhomme C, Laï JL, Demory JL, Caulier MT, Wattel E, Bordessoule D, Bauters F, Fenaux P. Acute myeloid leukemia and myelodysplastic syndromes following essential thrombocythemia treated with hydroxyurea: high proportion of cases with 17p deletion. Blood 1998; 91: 616-622, MEDLINE

3 Laï JL, Preudhomme M, Zandecki M, Flactif M, Vanrumbeke M, Lepelley P, Wattel E, Fenaux P. Myelodysplastic syndromes and acute myeloid leukemia with 17p deletion. An entity characterized by specific dysgranulopoiesis and a high incidence of p53 mutations. Leukemia 1995; 9: 370-381, MEDLINE

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5 Sedlacek SM, Curtis JL, Weintraub J, Levin J. Essential thrombocythemia and leukemic transformation. Medicine (Baltimore) 1986; 65: 353-364, MEDLINE

6 Andersson PO, Ridell B, Wadenvik H, Kutti J. Leukemic transformation of essential thrombocythemia without previous cytoreductive treatment. Ann Hematol 2000; 79: 40-42, MEDLINE

7 Rozman C, Giralt M, Feliu E, Rubio D, Cortes MT. Life expectancy of patients with chronic non-leukemic myeloproliferative disorders. Cancer 1991; 67: 2658-2663, MEDLINE