Endothelial cells express normal cellular prion protein

A 74-year-old man with slowly progressive leucopenia, macrocytic anaemia and thrombocytopenia over a 10-year period presented at our institution in September 2001 with a haemoglobin 9Æ8 g ⁄ dl (transfused), leucocyte count of 1Æ4 · 10 ⁄ l (18% neutrophils, 82% lymphocytes) and a platelet count of 42 · 10 ⁄ l without evidence of splenomegaly by examination. A bone marrow biopsy was hypercellular (80%) and demonstrated trilineage dysplasia with no increase in myeloblasts. Conventional G-banded chromosome analysis revealed a karyotype of 46,XY,del (20)(q13.1) in all 20 metaphases examined. The patient was given a diagnosis of refractory cytopenias with multilineage dysplasia (RCMD; International Prognostic Scoring System stage of intermediate-1; Greenberg et al, 1997), began a course of palliative erythropoietin for his anaemia and was followed. In July 2002, he developed an increased leucocyte count with marked circulating immature myeloid cells (leucocyte count 9Æ1 · 10 ⁄ l; 36% myelocytes, 12% metamyelocytes, 6% undifferentiated blasts, 9% progranulocytes, 16% segmented neutrophils, 26% lymphocytes and 1% monocytes), progressive splenomegaly, lymphadenopathy and new cutaneous lesions (erythematous plaques). Biopsy of the lymph nodes and skin lesions revealed infiltrating myeloid progenitors consistent with extramedullary haematopoiesis. A repeat bone marrow biopsy was markedly hypercellular (100%) with an increase in blasts (10%), suggesting progression of his myelodysplastic syndrome (MDS) to refractory anaemia with excess blasts. In comparing the two recent bone marrows, the morphological features were similar. Both were hypercellular on account of panhyperplasia with trilineage dysplasia. The most prominent changes were the development of neutrophilia and an increase in bone marrow blasts. Although frequent, small, hypolobated megakaryocytes were present in the second specimen, as often seen in chronic myeloid leukaemia (CML), they were also seen in the first specimen. Cytogenetic analysis again showed a deletion of chromosome 20q in each metaphase, but also the interval development of a subclone of cells (three out of 20 metaphases) with the karyotype 46,XY,del (20)(q13.1),t(9;22)(q34;q11.2). Similarly, fluorescent in situ hybridization (FISH) studies on peripheral blood showed 38Æ4% of 500 nuclei with BCR ⁄ABL fusion [double fusion FISH (D-FISH) strategy, normal < 1%]. Owing to the marked activity of imatinib mesylate (Gleevec; Novartis Pharmaceuticals, Hanover, NJ, USA) therapy in patients with CML and t(9;22)(q34;q11.2) (Druker et al, 2001), the patient was begun on imatinib mesylate therapy at 400 mg ⁄ d. The patient remained on imatinib for 6 months. During this time, the percentage of cells in his blood with BCR ⁄ABL fusion by FISH fell from 38Æ4% to a minimum of 9Æ8%. However, the patient had no improvement in his anaemia or thrombocytopenia. Indeed, additional attempts to escalate the dose of imatinib further, to gain a greater response, were hindered by dose-limiting thrombocytopenia. Secondary to the persistent thrombocytopenia, attempts were made to discontinue the imatinib mesylate, which resulted in marked leucocytosis (felt to be secondary to his CML phenotype) (130 · 10 ⁄ l) that resolved with reinstitution of therapy (see Fig 1), demonstrating that he did indeed manifest a CML phenotype concurrent with his MDS. In January 2003, the patient developed pneumonia and died. Post-mortem examination demonstrated an infiltration of myeloid progenitors in all major organs. The development of a Philadelphia chromosome associated with the typical t(9;22)(q34;q11.2) in patients with MDS is a very rare, but previously reported, event and is possibly a consequence of the acquired genetic instability associated with MDS (Verhoef et al, 1992). Goldberg et al (2003) recently reported the progression of an MDS subclone in a patient with CML treated with imatinib mesylate. Suppression of the Ph clone by imatinib mesylate led to a complete haematological response with respect to CML and normalization of marrow FISH-based studies for the BCRABL translocation, yet karyotyping revealed evolution of the MDS subclone in the marrow. In order to assess the frequency of patients with a t(9;22) subclone, a retrospective review of the Mayo Cytogenetics Laboratory database was performed (included both Mayo Clinic patients and