CASE REPORT

Acute myeloid leukaemia with t(8;21) associated with "occult" mastocytosis. Report of an unusual case and review of the literature

H-W Bernd¹, K Sotlar², J Lorenzen³, R Osieka⁴, U Fabry⁴, P Valent⁵ and H-P Horny¹

¹ Institute of Pathology, University of Lübeck, D-23538 Lübeck, Germany
² Institute of Pathology, University of Tübingen, D-72076 Tübingen, Germany
³ Institute of Pathology, University of Aachen, Aachen D-52074, Germany
⁴ Department of Internal Medicine IV, University of Aachen
⁵ Dept. of Internal Medicine I, Division of Haematology and Haemostaseology, University of Vienna, A-1090 Vienna, Austria

Correspondence to:
Correspondence to:
Professor H-P Horny
Institute of Pathology, Medical University of Lübeck, Ratzeburger Allee 160, D-23538 Lübeck, Germany; horny{at}patho.mu-luebeck.de

Approximately 20% of patients with systemic mastocytosis (SM) have an associated haematological, clonal, non-mast cell lineage disease, and most exhibit an associated myelogenous neoplasm. This report describes a 48 year old man with acute myeloid leukaemia (AML) and a type t(8;21) cytogenetic abnormality. Associated bone marrow mastocytosis (a defined subtype of SM) was only detected after successful polychemotherapy in the state of bone marrow aplasia, and persisted after complete remission of AML. The diagnosis of mastocytosis was based on the demonstration of a multifocal dense mastocytic infiltrate. The atypical mast cells showed prominent spindling and an aberrant immunophenotype, with coexpression of tryptase, chymase, KIT, and CD25—which is expressed only on neoplastic (not normal) mast cells. In addition, the transforming somatic mutation D816V of the c-kit gene was detected. Re-examination of the pretherapeutic (initial) bone marrow revealed a slight diffuse increase in partially spindle shaped mast cells also exhibiting an abnormal immunophenotype, with CD25 expression, although compact mastocytic infiltrates were not detected. Because the D816V mutation was detected in the initial bone marrow specimen, strict application of three minor diagnostic criteria (spindling, CD25, D816V) enabled a diagnosis of SM-AML to be confirmed retrospectively in the initial bone marrow tissue.

Keywords: mastocytosis; bone marrow; CD25; acute myeloid leukaemia; mast cell tryptase; occult; mastocytosis; c-kit mutation

Abbreviations: AHNMD, associated haematological clonal non-mast cell lineage disease; AML, acute myeloid leukaemia; PNA, peptide nucleic acid; WHO, World Health Organisation

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